Substitution Effects and Electronic Properties of the Azo Dye

(1-phenylazo-2-naphthol) Species A TD-DFT Electronic Spectra Investigation

Lakhdar Mansouria and Bachir Zouchouneab

a Laboratoire de Chimie appliqueacutee et Technologie des Mateacuteriaux Universiteacute Larbi Ben

MrsquoHidi-Oum el Bouaghi (04000) Oum el Bouaghi Algeacuterie

b Uniteacute de Recherche de Chimie de lrsquoEnvironnement et Moleacuteculaire Structurale Universiteacute-

Constantine 1 (ex Mentouri-Constantine) (25000) Constantine Algeacuterie

E-mail bzouchouneuniv-oebdz Tel (213) 6 62 03 81 83 Fax (213) 32 42 83 39

Corresponding author

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Abstract

DFTB3LYP and ab initio HF calculations with full geometry optimization have been carried

out on hydrazo azo forms of 1-phenylazo-2-naphthol and their substituted derivatives The

predicted geometries show a small energy difference of 18 kcalmol might tune the

equilibrium between both forms Depending on the electron-donating and electron-accepting

of the different used substituents (CF3 NH2 CH3 Cl and NO2) the various obtained isomers

show small energy differencies between meta and para substitution except for the NH2 one

indicating the co-existence of the tautomers in solution The ortho(C12) position was revealed

to be the less favored substitution in all cases while the second ortho(C16) position for

different substituents provides isomers competing the most stable meta and para ones The

obtained results suggest that a judicious choice in the substituentsrsquo use on the phenyl ring

should lead to stabilization The TD-DFT theoretical study performed on the optimized

geometry allowed us to identify quite clearly the spectral position and the nature of the

different electronic transitions according to their molecular orbitals localization hence

reproducing the available UV-Vis spectra The increase in the wavelength values is in perfect

agreement with red shifts and the ∆E (ELUMO-EHOMO) decreasing Thus both from the point of

view of substitution and the used solvent the obtained electronic spectra appear to behave

quite differently

Keywords

Azo dye Tautomers Electronic structure Electronic transitions Molecular orbital

localization Density functional theory

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Introduction

Azo compounds are versatile molecules and have received much interest in research in the

view of both fundamental and application fields1-3 From part of an extended class of

synthetic dyes which have shown potential applications not only as textile colorants but in

many important domains such as molecular sensing4 data storage5 nonlinear optics6

adsorption chromatography7 and biochemical due to their capability to bind proteins8

The importance in this specific group of chromophores lies in the relative simplicity of

their synthesis in the derivatization sublimation fastness light-fastness and in the exhibition

of a large variety of bright colors Usually the azo group is attached to benzene and

naphthalene rings but it can be bonded as well to aromatic heterocycles or enolizable aliphatic

moieties which have been theoretically and experimentally investigated in recent works9-12

The dye characteristics such as solubility or color present several variations which arise from

the effect of various groups that are attached to the aromatic ring1314 Since the aromatic

moieties attached to the azo group help to stabilize the N=N group by making it part of an

extended delocalized system they often absorb visible frequencies of light Several

investigations were dedicated to the synthesis and the spectroscopic characterization of dyes

as to evaluate and to develop their physical and chemical properties1516

Azo dyes are also of particular interest to chemists because they can be easily prepared

with a wide range of donor and acceptor groups Besides the planarity of the azo bridge is

expected to promote the electronic delocalization and increase the absorption strength17minus20

Depending on the tautomers two types of intra-molecular hydrogen bonds are possible Ondash

HbullbullbullN and NndashHbullbullbullO respectively in azo and hydrazone tautomers The azo-hydrazone

tautomerism in azo dyes has been known for more than a hundred years as a chemical

equilibrium between azo and hydrazo forms The interconversion of both forms provokes the

movement of a proton and the shifting of bonding electrons thus the isomerism is considered

as tautomerism leading to different properties between the two forms where a strong

hydrogen bond enhanced by resonance is set inducing the azo-hydrazone tautomeric shift

Over the years the problem of the OndashHbullbullbullN NndashHbullbullbullO competition in azonaphtols has also

prompted a number of studies based on NMR17 or absorption and fluorescence spectroscopy18

Another form of azo compounds is the zwitterionic form which has an ionic intra-molecular

hydrogen bond (N+ndashHmiddot middot middotO-) and whose N+ndashH bond length is longer than the standard

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interatomic distance observed in neutral NndashH bond

The 1-phenylazo-2-naphthol is the purpose of this study is among the azo species

which has been theoretically and experimentally investigated and widely used as well as its

derivatives19 Still there is no comprehensive overview on their electronic structure

properties and substitution effects so far This is what we endeavor to show in this paper

through a theoretical study provided by means of DFT HF and TD-DFT methods All the

optimized geometries have been carried out using the HF and B3LYP functional which has

been shown to reproduce efficiently the experimental structure but the results always remain

depending on the level of theory and the used basis set

Results and discussion

Geometry optimization

Unsubstituted species

The full geometry optimizations were carried out on the hydrazo and azo forms of 1-

phenylazo-2-naphthol in gas phase The obtained structures are displayed in Fig 1 with

atom-numbering shown in Scheme 1 (a and b) while the geometrical and energetic

parameters are gathered in Tables 1-3 The 1-phenylazo-2-naphthol in its hydrazo form has

been structurally characterized by X-ray diffraction since more than three decades24-26

The obtained results demonstrate a small energy difference between both structures a

and b of 18 and 08 kcalmol in favour of the hydrazo form obtained by B3LYP and HF

methods respectively using the same basis set for better description (See computational

details) These results are comparable to previously carried out theoretical studies using AM1

and ab initio calculations and exhibiting large HOMO-LUMO gaps of 302 and 319 eV

respectively27 as shown in Fig 2 Thus confirming the tautomers interconverting in solution

The thermodynamic measure of molecular stability is H which gives the enthalpy of the

compound relative to the reference state of its constituent elements under standard conditions

The thermodynamic data obtained by our DFT calculations provide an opportunity to

establish a stability order between different isomers as displayed in Fig 1 Indeed the ∆H

has the meaning of energy difference between the two OndashHbullbullbullN and NndashHbullbullbullO ground-state

vibrational levels corroborating the stability order discussed above concerning the trend of the

total bonding energy (TBE) The migration of the proton between the oxygen and the nitrogen

atoms in the azo and the hydrazo forms respectively does not require an important energy

barrier as shown in Scheme 2 where the transition state is separated from the azo and

hydrazone forms only by 04 and 22 kcalmol respectively Accordingly when the

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geometries of the azo hydrazo and transition state are compared one can see the reduction of

the NbullbullbullO distance of the transition state of 2463 Aring with regard to the initial and the final

forms of 2645 and 2718 Aring (B3LYP) respectively For the transition state the ObullbullbullH and

HbullbullbullN distances become 1207 and 1256 Aring respectively as compared to initial azo form

values of 1006 and 1639 Aring and those of the final hydrazone form of 1683 and 1035 Aring

respectively The predominance of the hydrazo form has been suggested by many previous

studies using X-ray photoelectron spectroscopy and diffuse reflectance of the solids2829 The

occurring migration affects scarcely the phenyl ring where a delocalized scheme is present in

both forms but one naphthylrsquos ring of the hydrazo form undergoes significant changes

displaying a clear localized scheme with long C1-C6 and C5-C6 and short C4-C5 bond lengths

of 1470 1448 and 1350 Aring respectively while a localized scheme is present in both

naphthyl rings for the azo form as displayed by the average C-C bond distance gathered in

Tables 12 It is worthwhile indicating that the hydrogen migration gives rise to noticeable

structural variations in the vicinity of the azo group for the hydrazo form which can be

evidenced by the bond lengths of N1-N2 (1300 Aring) C11-N2 (1397 Aring) C2-N1 (1323 Aring) N2-H

(1035 Aring) C-O (1256 Aring) and ObullbullbullH interaction of 1683 Aring compared to those obtained for

the azo form given by the following bond distances N1-N2 (1268 Aring) C11-N2 (1409 Aring) C2-

N1 (1379 Aring) O-H (1006 Aring) C-O (1336 Aring) and N2bullbullbullH interaction of 1639 Aring Generally for

the azo form the N-N double bond length is 1250 Aring3031 slightly shorter than that found by

our calculations Itrsquos noticeable that in the azo form the aromatic phenyl and the naphthyl

rings are oriented to each other by (θ = 200deg) whereas they are coplanar in the hydrazo form

(θ = 10deg) where θ is the C3C2C11C16 dihedral angle The twist in the azo form can be likely

explained by the weak delocalization over the C11-N2 (1409 Aring) and C2-N1 (1379 Aring) bonds

However the flatness of the hydrazo form helps the extension of the delocalization of the

system It is worth noting that the calculated geometrical parameters are comparable to those

observed experimentally in previous works2425

The HF results do not show severe discrepancies with regard to those obtained by the

DFTB3LYP method In general the geometrical parameters gathered in Tables 12 display

similarities between B3LYP and HF but the largest discrepancy is calculated for the N=N

bond distance in the azo form which deviates by 005 Aring (1219 Aring) than that obtained by

B3LYP (1268 Aring) The energetic data show also the same tendency to that obtained by

B3LYP but with reduced relative energy values as clearly displayed in Fig 2 and Tables 3

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It can be said that the formation of the intramolecular NminusHbullbullbullO hydrogen bond should

contribute to stabilize slightly the hydrazo form in agreement with previous experimental

results3233

Substitution effects

For this purpose we will be interested in this part in giving a deeper insight to the role

likely to be played by the various substituents (CH3 CF3 NH2 Cl and NO2) used according to

their electronic properties because azo dyes can be easily prepared with a wide range of

donor and acceptor groups

We analyze by means of the density functional theory (DFT) and HF calculations all

possible predicted isomers carried out on the hydrazo form The different isomers are

obtained alternately by substitution on the carbon sites belonging to the phenyl ring namely

C12 and C16 (ortho) C13 and C15 (meta) and C14 (para) atoms positions (Fig 3) respectively in

order to evaluate the electron donating and accepting abilities of each used substituent and to

establish a stability order for each substitution

One can observe that the bond lengths vary slightly from one isomer to other for each

substitution The different substituents provoke shortening or lengthening of the bond

distances in accordance with either the electron-withdrawing or the electron-donating

characters respectively The findings displayed in Fig 3 show clearly that the ortho(C12)

position is the less favored in all cases giving rise to isomers which are less stable than their

analogs ortho(C16) meta and para ones It is worth to mention that the meta(C15) isomers are

not discussed in this work because of their similarities of those obtained for meta(C13) ones

thus we contented only with presenting the results of the latter On the other hand these

results highlight a hard competition between para and meta isomers except for the NH2 For

the chlorine substitution the para-Cl isomer lies at the same energy than the meta-Cl one

The latter isomer was recently synthesized and characterized by X-ray diffraction revealing a

comparative geometrical parameters than our theoretical findings34 However the ortho(C12)-

Cl isomer is less stable by 74 kcalmol than the para-Cl and meta-Cl ones but the ortho(C16)-

Cl isomer is more stable than its analogous substituted on C16 position by 48 kcalmol

stabilized by NndashHbullbullbullCl interactions It is worth noting that the calculated bond distances

within the phenyl ring for the para-Cl isomer are somewhat shortened compared to those of

the unsubstituted hydrazo form evidenced by the average C-C bond distances as displayed in

Tables 12 This reports the predicted structure parameters and the available experimental

data inversely to the withdrawing property of chlorine the N-N and C-N bonds are not

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affected The less stable ortho(C12)-Cl isomer exhibits a distorted structure with a dihedral

C3C2C11C16 angle of 444deg Indeed this twisted geometry stemmes essentially from strong

repulsions between the azo group and the chlorine atom whose the average Cl-N2 overlap

population is evaluated as negative value of -0056 (Fig 3) despite of the long distance of

3045 Aring Contrarily to the other substitutions there is no competition between para-NH2 and

meta-NH2 where the former isomer is more stable than the latter one by 101 kcalmol So

the following stability order is established para-NH2 gt ortho(C15)-NH2 gt meta-NH2 gt

ortho(C12)-NH2 Surprisingly NH2 as donor substituent is expected to decrease bond

distances within the attached phenyl ring however slight lengthening for these bond

distances are calculated as displayed in Tables 12 thereby the electron density on the

aromatic ring is reduced For the NO2 CF3 and CH3 no noticeable variations are emphasized

(Tables 12) It is interesting to indicate that NO2 (para red) derivative has been synthesized

and characterized several years ago35 Regarding the CH3 substitution the obtained isomers

lie almost at the same energy with small deviation for the ortho(C12)-CH3 isomer which was

found above the more stable meta and para isomers by 38 kcalmol and 33 kcalmol than the

ortho-CH3(C16) one This weak instability arises from the presence of interactions between

CH3 and the azo group revealing an average positive overlap population for the N-H(CH3)

contacts However the meta isomer is disfavored by the enthalpy and the Gibbs free energy

(∆H = 82 and ∆G = 94 kcalmol) The obtained DFT results match well with the combined

X-ray and NMR analysis on phenyl substituted suggesting that electron-withdrawing

substituent like NO225 and Cl36 stabilize the hydrazo form at para position Mulliken

population analysis has been provided in order to evaluate electron-donating or electron-

withdrawing effects of the used substitions at the para position The attached substituent is

connected to the phenyl ring through C(14) carbon atom where its net charge endure

modifications in accordance with the electron-donating or electron-withdrawing Indeed

Mulliken atomic net charges are used to estimate atomic charges and since these values

evaluate the electronic effects of different substituents A consistent trend can be seen in

Table 1 from the values collected using B3LYP method for para substitution The comparison

is based on the atomic net charges of the C(14) carbon atom before (+0 101) and after

substitution One can observe the decreasing of positive charge on C(14) atom in the order of

NO2 (+0140) gt CF3 (+0129) gt Cl (+0113) gt NH2 (+0080) gt CH3 (+0050) emphasizing the

electron-withdrawing effect increasing from CH3 to NO2 It can be seen from the Table 1 that

NO2 has the strongest electron-withdrawing effect which significantly decreases the

electronegativity of C(14) while the CH3 has the strongest electron-donating effect which

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

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10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

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10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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Abstract

DFTB3LYP and ab initio HF calculations with full geometry optimization have been carried

out on hydrazo azo forms of 1-phenylazo-2-naphthol and their substituted derivatives The

predicted geometries show a small energy difference of 18 kcalmol might tune the

equilibrium between both forms Depending on the electron-donating and electron-accepting

of the different used substituents (CF3 NH2 CH3 Cl and NO2) the various obtained isomers

show small energy differencies between meta and para substitution except for the NH2 one

indicating the co-existence of the tautomers in solution The ortho(C12) position was revealed

to be the less favored substitution in all cases while the second ortho(C16) position for

different substituents provides isomers competing the most stable meta and para ones The

obtained results suggest that a judicious choice in the substituentsrsquo use on the phenyl ring

should lead to stabilization The TD-DFT theoretical study performed on the optimized

geometry allowed us to identify quite clearly the spectral position and the nature of the

different electronic transitions according to their molecular orbitals localization hence

reproducing the available UV-Vis spectra The increase in the wavelength values is in perfect

agreement with red shifts and the ∆E (ELUMO-EHOMO) decreasing Thus both from the point of

view of substitution and the used solvent the obtained electronic spectra appear to behave

quite differently

Keywords

Azo dye Tautomers Electronic structure Electronic transitions Molecular orbital

localization Density functional theory

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Introduction

Azo compounds are versatile molecules and have received much interest in research in the

view of both fundamental and application fields1-3 From part of an extended class of

synthetic dyes which have shown potential applications not only as textile colorants but in

many important domains such as molecular sensing4 data storage5 nonlinear optics6

adsorption chromatography7 and biochemical due to their capability to bind proteins8

The importance in this specific group of chromophores lies in the relative simplicity of

their synthesis in the derivatization sublimation fastness light-fastness and in the exhibition

of a large variety of bright colors Usually the azo group is attached to benzene and

naphthalene rings but it can be bonded as well to aromatic heterocycles or enolizable aliphatic

moieties which have been theoretically and experimentally investigated in recent works9-12

The dye characteristics such as solubility or color present several variations which arise from

the effect of various groups that are attached to the aromatic ring1314 Since the aromatic

moieties attached to the azo group help to stabilize the N=N group by making it part of an

extended delocalized system they often absorb visible frequencies of light Several

investigations were dedicated to the synthesis and the spectroscopic characterization of dyes

as to evaluate and to develop their physical and chemical properties1516

Azo dyes are also of particular interest to chemists because they can be easily prepared

with a wide range of donor and acceptor groups Besides the planarity of the azo bridge is

expected to promote the electronic delocalization and increase the absorption strength17minus20

Depending on the tautomers two types of intra-molecular hydrogen bonds are possible Ondash

HbullbullbullN and NndashHbullbullbullO respectively in azo and hydrazone tautomers The azo-hydrazone

tautomerism in azo dyes has been known for more than a hundred years as a chemical

equilibrium between azo and hydrazo forms The interconversion of both forms provokes the

movement of a proton and the shifting of bonding electrons thus the isomerism is considered

as tautomerism leading to different properties between the two forms where a strong

hydrogen bond enhanced by resonance is set inducing the azo-hydrazone tautomeric shift

Over the years the problem of the OndashHbullbullbullN NndashHbullbullbullO competition in azonaphtols has also

prompted a number of studies based on NMR17 or absorption and fluorescence spectroscopy18

Another form of azo compounds is the zwitterionic form which has an ionic intra-molecular

hydrogen bond (N+ndashHmiddot middot middotO-) and whose N+ndashH bond length is longer than the standard

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interatomic distance observed in neutral NndashH bond

The 1-phenylazo-2-naphthol is the purpose of this study is among the azo species

which has been theoretically and experimentally investigated and widely used as well as its

derivatives19 Still there is no comprehensive overview on their electronic structure

properties and substitution effects so far This is what we endeavor to show in this paper

through a theoretical study provided by means of DFT HF and TD-DFT methods All the

optimized geometries have been carried out using the HF and B3LYP functional which has

been shown to reproduce efficiently the experimental structure but the results always remain

depending on the level of theory and the used basis set

Results and discussion

Geometry optimization

Unsubstituted species

The full geometry optimizations were carried out on the hydrazo and azo forms of 1-

phenylazo-2-naphthol in gas phase The obtained structures are displayed in Fig 1 with

atom-numbering shown in Scheme 1 (a and b) while the geometrical and energetic

parameters are gathered in Tables 1-3 The 1-phenylazo-2-naphthol in its hydrazo form has

been structurally characterized by X-ray diffraction since more than three decades24-26

The obtained results demonstrate a small energy difference between both structures a

and b of 18 and 08 kcalmol in favour of the hydrazo form obtained by B3LYP and HF

methods respectively using the same basis set for better description (See computational

details) These results are comparable to previously carried out theoretical studies using AM1

and ab initio calculations and exhibiting large HOMO-LUMO gaps of 302 and 319 eV

respectively27 as shown in Fig 2 Thus confirming the tautomers interconverting in solution

The thermodynamic measure of molecular stability is H which gives the enthalpy of the

compound relative to the reference state of its constituent elements under standard conditions

The thermodynamic data obtained by our DFT calculations provide an opportunity to

establish a stability order between different isomers as displayed in Fig 1 Indeed the ∆H

has the meaning of energy difference between the two OndashHbullbullbullN and NndashHbullbullbullO ground-state

vibrational levels corroborating the stability order discussed above concerning the trend of the

total bonding energy (TBE) The migration of the proton between the oxygen and the nitrogen

atoms in the azo and the hydrazo forms respectively does not require an important energy

barrier as shown in Scheme 2 where the transition state is separated from the azo and

hydrazone forms only by 04 and 22 kcalmol respectively Accordingly when the

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geometries of the azo hydrazo and transition state are compared one can see the reduction of

the NbullbullbullO distance of the transition state of 2463 Aring with regard to the initial and the final

forms of 2645 and 2718 Aring (B3LYP) respectively For the transition state the ObullbullbullH and

HbullbullbullN distances become 1207 and 1256 Aring respectively as compared to initial azo form

values of 1006 and 1639 Aring and those of the final hydrazone form of 1683 and 1035 Aring

respectively The predominance of the hydrazo form has been suggested by many previous

studies using X-ray photoelectron spectroscopy and diffuse reflectance of the solids2829 The

occurring migration affects scarcely the phenyl ring where a delocalized scheme is present in

both forms but one naphthylrsquos ring of the hydrazo form undergoes significant changes

displaying a clear localized scheme with long C1-C6 and C5-C6 and short C4-C5 bond lengths

of 1470 1448 and 1350 Aring respectively while a localized scheme is present in both

naphthyl rings for the azo form as displayed by the average C-C bond distance gathered in

Tables 12 It is worthwhile indicating that the hydrogen migration gives rise to noticeable

structural variations in the vicinity of the azo group for the hydrazo form which can be

evidenced by the bond lengths of N1-N2 (1300 Aring) C11-N2 (1397 Aring) C2-N1 (1323 Aring) N2-H

(1035 Aring) C-O (1256 Aring) and ObullbullbullH interaction of 1683 Aring compared to those obtained for

the azo form given by the following bond distances N1-N2 (1268 Aring) C11-N2 (1409 Aring) C2-

N1 (1379 Aring) O-H (1006 Aring) C-O (1336 Aring) and N2bullbullbullH interaction of 1639 Aring Generally for

the azo form the N-N double bond length is 1250 Aring3031 slightly shorter than that found by

our calculations Itrsquos noticeable that in the azo form the aromatic phenyl and the naphthyl

rings are oriented to each other by (θ = 200deg) whereas they are coplanar in the hydrazo form

(θ = 10deg) where θ is the C3C2C11C16 dihedral angle The twist in the azo form can be likely

explained by the weak delocalization over the C11-N2 (1409 Aring) and C2-N1 (1379 Aring) bonds

However the flatness of the hydrazo form helps the extension of the delocalization of the

system It is worth noting that the calculated geometrical parameters are comparable to those

observed experimentally in previous works2425

The HF results do not show severe discrepancies with regard to those obtained by the

DFTB3LYP method In general the geometrical parameters gathered in Tables 12 display

similarities between B3LYP and HF but the largest discrepancy is calculated for the N=N

bond distance in the azo form which deviates by 005 Aring (1219 Aring) than that obtained by

B3LYP (1268 Aring) The energetic data show also the same tendency to that obtained by

B3LYP but with reduced relative energy values as clearly displayed in Fig 2 and Tables 3

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It can be said that the formation of the intramolecular NminusHbullbullbullO hydrogen bond should

contribute to stabilize slightly the hydrazo form in agreement with previous experimental

results3233

Substitution effects

For this purpose we will be interested in this part in giving a deeper insight to the role

likely to be played by the various substituents (CH3 CF3 NH2 Cl and NO2) used according to

their electronic properties because azo dyes can be easily prepared with a wide range of

donor and acceptor groups

We analyze by means of the density functional theory (DFT) and HF calculations all

possible predicted isomers carried out on the hydrazo form The different isomers are

obtained alternately by substitution on the carbon sites belonging to the phenyl ring namely

C12 and C16 (ortho) C13 and C15 (meta) and C14 (para) atoms positions (Fig 3) respectively in

order to evaluate the electron donating and accepting abilities of each used substituent and to

establish a stability order for each substitution

One can observe that the bond lengths vary slightly from one isomer to other for each

substitution The different substituents provoke shortening or lengthening of the bond

distances in accordance with either the electron-withdrawing or the electron-donating

characters respectively The findings displayed in Fig 3 show clearly that the ortho(C12)

position is the less favored in all cases giving rise to isomers which are less stable than their

analogs ortho(C16) meta and para ones It is worth to mention that the meta(C15) isomers are

not discussed in this work because of their similarities of those obtained for meta(C13) ones

thus we contented only with presenting the results of the latter On the other hand these

results highlight a hard competition between para and meta isomers except for the NH2 For

the chlorine substitution the para-Cl isomer lies at the same energy than the meta-Cl one

The latter isomer was recently synthesized and characterized by X-ray diffraction revealing a

comparative geometrical parameters than our theoretical findings34 However the ortho(C12)-

Cl isomer is less stable by 74 kcalmol than the para-Cl and meta-Cl ones but the ortho(C16)-

Cl isomer is more stable than its analogous substituted on C16 position by 48 kcalmol

stabilized by NndashHbullbullbullCl interactions It is worth noting that the calculated bond distances

within the phenyl ring for the para-Cl isomer are somewhat shortened compared to those of

the unsubstituted hydrazo form evidenced by the average C-C bond distances as displayed in

Tables 12 This reports the predicted structure parameters and the available experimental

data inversely to the withdrawing property of chlorine the N-N and C-N bonds are not

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affected The less stable ortho(C12)-Cl isomer exhibits a distorted structure with a dihedral

C3C2C11C16 angle of 444deg Indeed this twisted geometry stemmes essentially from strong

repulsions between the azo group and the chlorine atom whose the average Cl-N2 overlap

population is evaluated as negative value of -0056 (Fig 3) despite of the long distance of

3045 Aring Contrarily to the other substitutions there is no competition between para-NH2 and

meta-NH2 where the former isomer is more stable than the latter one by 101 kcalmol So

the following stability order is established para-NH2 gt ortho(C15)-NH2 gt meta-NH2 gt

ortho(C12)-NH2 Surprisingly NH2 as donor substituent is expected to decrease bond

distances within the attached phenyl ring however slight lengthening for these bond

distances are calculated as displayed in Tables 12 thereby the electron density on the

aromatic ring is reduced For the NO2 CF3 and CH3 no noticeable variations are emphasized

(Tables 12) It is interesting to indicate that NO2 (para red) derivative has been synthesized

and characterized several years ago35 Regarding the CH3 substitution the obtained isomers

lie almost at the same energy with small deviation for the ortho(C12)-CH3 isomer which was

found above the more stable meta and para isomers by 38 kcalmol and 33 kcalmol than the

ortho-CH3(C16) one This weak instability arises from the presence of interactions between

CH3 and the azo group revealing an average positive overlap population for the N-H(CH3)

contacts However the meta isomer is disfavored by the enthalpy and the Gibbs free energy

(∆H = 82 and ∆G = 94 kcalmol) The obtained DFT results match well with the combined

X-ray and NMR analysis on phenyl substituted suggesting that electron-withdrawing

substituent like NO225 and Cl36 stabilize the hydrazo form at para position Mulliken

population analysis has been provided in order to evaluate electron-donating or electron-

withdrawing effects of the used substitions at the para position The attached substituent is

connected to the phenyl ring through C(14) carbon atom where its net charge endure

modifications in accordance with the electron-donating or electron-withdrawing Indeed

Mulliken atomic net charges are used to estimate atomic charges and since these values

evaluate the electronic effects of different substituents A consistent trend can be seen in

Table 1 from the values collected using B3LYP method for para substitution The comparison

is based on the atomic net charges of the C(14) carbon atom before (+0 101) and after

substitution One can observe the decreasing of positive charge on C(14) atom in the order of

NO2 (+0140) gt CF3 (+0129) gt Cl (+0113) gt NH2 (+0080) gt CH3 (+0050) emphasizing the

electron-withdrawing effect increasing from CH3 to NO2 It can be seen from the Table 1 that

NO2 has the strongest electron-withdrawing effect which significantly decreases the

electronegativity of C(14) while the CH3 has the strongest electron-donating effect which

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

Page 20 of 26C

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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Page 24 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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Introduction

Azo compounds are versatile molecules and have received much interest in research in the

view of both fundamental and application fields1-3 From part of an extended class of

synthetic dyes which have shown potential applications not only as textile colorants but in

many important domains such as molecular sensing4 data storage5 nonlinear optics6

adsorption chromatography7 and biochemical due to their capability to bind proteins8

The importance in this specific group of chromophores lies in the relative simplicity of

their synthesis in the derivatization sublimation fastness light-fastness and in the exhibition

of a large variety of bright colors Usually the azo group is attached to benzene and

naphthalene rings but it can be bonded as well to aromatic heterocycles or enolizable aliphatic

moieties which have been theoretically and experimentally investigated in recent works9-12

The dye characteristics such as solubility or color present several variations which arise from

the effect of various groups that are attached to the aromatic ring1314 Since the aromatic

moieties attached to the azo group help to stabilize the N=N group by making it part of an

extended delocalized system they often absorb visible frequencies of light Several

investigations were dedicated to the synthesis and the spectroscopic characterization of dyes

as to evaluate and to develop their physical and chemical properties1516

Azo dyes are also of particular interest to chemists because they can be easily prepared

with a wide range of donor and acceptor groups Besides the planarity of the azo bridge is

expected to promote the electronic delocalization and increase the absorption strength17minus20

Depending on the tautomers two types of intra-molecular hydrogen bonds are possible Ondash

HbullbullbullN and NndashHbullbullbullO respectively in azo and hydrazone tautomers The azo-hydrazone

tautomerism in azo dyes has been known for more than a hundred years as a chemical

equilibrium between azo and hydrazo forms The interconversion of both forms provokes the

movement of a proton and the shifting of bonding electrons thus the isomerism is considered

as tautomerism leading to different properties between the two forms where a strong

hydrogen bond enhanced by resonance is set inducing the azo-hydrazone tautomeric shift

Over the years the problem of the OndashHbullbullbullN NndashHbullbullbullO competition in azonaphtols has also

prompted a number of studies based on NMR17 or absorption and fluorescence spectroscopy18

Another form of azo compounds is the zwitterionic form which has an ionic intra-molecular

hydrogen bond (N+ndashHmiddot middot middotO-) and whose N+ndashH bond length is longer than the standard

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interatomic distance observed in neutral NndashH bond

The 1-phenylazo-2-naphthol is the purpose of this study is among the azo species

which has been theoretically and experimentally investigated and widely used as well as its

derivatives19 Still there is no comprehensive overview on their electronic structure

properties and substitution effects so far This is what we endeavor to show in this paper

through a theoretical study provided by means of DFT HF and TD-DFT methods All the

optimized geometries have been carried out using the HF and B3LYP functional which has

been shown to reproduce efficiently the experimental structure but the results always remain

depending on the level of theory and the used basis set

Results and discussion

Geometry optimization

Unsubstituted species

The full geometry optimizations were carried out on the hydrazo and azo forms of 1-

phenylazo-2-naphthol in gas phase The obtained structures are displayed in Fig 1 with

atom-numbering shown in Scheme 1 (a and b) while the geometrical and energetic

parameters are gathered in Tables 1-3 The 1-phenylazo-2-naphthol in its hydrazo form has

been structurally characterized by X-ray diffraction since more than three decades24-26

The obtained results demonstrate a small energy difference between both structures a

and b of 18 and 08 kcalmol in favour of the hydrazo form obtained by B3LYP and HF

methods respectively using the same basis set for better description (See computational

details) These results are comparable to previously carried out theoretical studies using AM1

and ab initio calculations and exhibiting large HOMO-LUMO gaps of 302 and 319 eV

respectively27 as shown in Fig 2 Thus confirming the tautomers interconverting in solution

The thermodynamic measure of molecular stability is H which gives the enthalpy of the

compound relative to the reference state of its constituent elements under standard conditions

The thermodynamic data obtained by our DFT calculations provide an opportunity to

establish a stability order between different isomers as displayed in Fig 1 Indeed the ∆H

has the meaning of energy difference between the two OndashHbullbullbullN and NndashHbullbullbullO ground-state

vibrational levels corroborating the stability order discussed above concerning the trend of the

total bonding energy (TBE) The migration of the proton between the oxygen and the nitrogen

atoms in the azo and the hydrazo forms respectively does not require an important energy

barrier as shown in Scheme 2 where the transition state is separated from the azo and

hydrazone forms only by 04 and 22 kcalmol respectively Accordingly when the

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geometries of the azo hydrazo and transition state are compared one can see the reduction of

the NbullbullbullO distance of the transition state of 2463 Aring with regard to the initial and the final

forms of 2645 and 2718 Aring (B3LYP) respectively For the transition state the ObullbullbullH and

HbullbullbullN distances become 1207 and 1256 Aring respectively as compared to initial azo form

values of 1006 and 1639 Aring and those of the final hydrazone form of 1683 and 1035 Aring

respectively The predominance of the hydrazo form has been suggested by many previous

studies using X-ray photoelectron spectroscopy and diffuse reflectance of the solids2829 The

occurring migration affects scarcely the phenyl ring where a delocalized scheme is present in

both forms but one naphthylrsquos ring of the hydrazo form undergoes significant changes

displaying a clear localized scheme with long C1-C6 and C5-C6 and short C4-C5 bond lengths

of 1470 1448 and 1350 Aring respectively while a localized scheme is present in both

naphthyl rings for the azo form as displayed by the average C-C bond distance gathered in

Tables 12 It is worthwhile indicating that the hydrogen migration gives rise to noticeable

structural variations in the vicinity of the azo group for the hydrazo form which can be

evidenced by the bond lengths of N1-N2 (1300 Aring) C11-N2 (1397 Aring) C2-N1 (1323 Aring) N2-H

(1035 Aring) C-O (1256 Aring) and ObullbullbullH interaction of 1683 Aring compared to those obtained for

the azo form given by the following bond distances N1-N2 (1268 Aring) C11-N2 (1409 Aring) C2-

N1 (1379 Aring) O-H (1006 Aring) C-O (1336 Aring) and N2bullbullbullH interaction of 1639 Aring Generally for

the azo form the N-N double bond length is 1250 Aring3031 slightly shorter than that found by

our calculations Itrsquos noticeable that in the azo form the aromatic phenyl and the naphthyl

rings are oriented to each other by (θ = 200deg) whereas they are coplanar in the hydrazo form

(θ = 10deg) where θ is the C3C2C11C16 dihedral angle The twist in the azo form can be likely

explained by the weak delocalization over the C11-N2 (1409 Aring) and C2-N1 (1379 Aring) bonds

However the flatness of the hydrazo form helps the extension of the delocalization of the

system It is worth noting that the calculated geometrical parameters are comparable to those

observed experimentally in previous works2425

The HF results do not show severe discrepancies with regard to those obtained by the

DFTB3LYP method In general the geometrical parameters gathered in Tables 12 display

similarities between B3LYP and HF but the largest discrepancy is calculated for the N=N

bond distance in the azo form which deviates by 005 Aring (1219 Aring) than that obtained by

B3LYP (1268 Aring) The energetic data show also the same tendency to that obtained by

B3LYP but with reduced relative energy values as clearly displayed in Fig 2 and Tables 3

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It can be said that the formation of the intramolecular NminusHbullbullbullO hydrogen bond should

contribute to stabilize slightly the hydrazo form in agreement with previous experimental

results3233

Substitution effects

For this purpose we will be interested in this part in giving a deeper insight to the role

likely to be played by the various substituents (CH3 CF3 NH2 Cl and NO2) used according to

their electronic properties because azo dyes can be easily prepared with a wide range of

donor and acceptor groups

We analyze by means of the density functional theory (DFT) and HF calculations all

possible predicted isomers carried out on the hydrazo form The different isomers are

obtained alternately by substitution on the carbon sites belonging to the phenyl ring namely

C12 and C16 (ortho) C13 and C15 (meta) and C14 (para) atoms positions (Fig 3) respectively in

order to evaluate the electron donating and accepting abilities of each used substituent and to

establish a stability order for each substitution

One can observe that the bond lengths vary slightly from one isomer to other for each

substitution The different substituents provoke shortening or lengthening of the bond

distances in accordance with either the electron-withdrawing or the electron-donating

characters respectively The findings displayed in Fig 3 show clearly that the ortho(C12)

position is the less favored in all cases giving rise to isomers which are less stable than their

analogs ortho(C16) meta and para ones It is worth to mention that the meta(C15) isomers are

not discussed in this work because of their similarities of those obtained for meta(C13) ones

thus we contented only with presenting the results of the latter On the other hand these

results highlight a hard competition between para and meta isomers except for the NH2 For

the chlorine substitution the para-Cl isomer lies at the same energy than the meta-Cl one

The latter isomer was recently synthesized and characterized by X-ray diffraction revealing a

comparative geometrical parameters than our theoretical findings34 However the ortho(C12)-

Cl isomer is less stable by 74 kcalmol than the para-Cl and meta-Cl ones but the ortho(C16)-

Cl isomer is more stable than its analogous substituted on C16 position by 48 kcalmol

stabilized by NndashHbullbullbullCl interactions It is worth noting that the calculated bond distances

within the phenyl ring for the para-Cl isomer are somewhat shortened compared to those of

the unsubstituted hydrazo form evidenced by the average C-C bond distances as displayed in

Tables 12 This reports the predicted structure parameters and the available experimental

data inversely to the withdrawing property of chlorine the N-N and C-N bonds are not

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affected The less stable ortho(C12)-Cl isomer exhibits a distorted structure with a dihedral

C3C2C11C16 angle of 444deg Indeed this twisted geometry stemmes essentially from strong

repulsions between the azo group and the chlorine atom whose the average Cl-N2 overlap

population is evaluated as negative value of -0056 (Fig 3) despite of the long distance of

3045 Aring Contrarily to the other substitutions there is no competition between para-NH2 and

meta-NH2 where the former isomer is more stable than the latter one by 101 kcalmol So

the following stability order is established para-NH2 gt ortho(C15)-NH2 gt meta-NH2 gt

ortho(C12)-NH2 Surprisingly NH2 as donor substituent is expected to decrease bond

distances within the attached phenyl ring however slight lengthening for these bond

distances are calculated as displayed in Tables 12 thereby the electron density on the

aromatic ring is reduced For the NO2 CF3 and CH3 no noticeable variations are emphasized

(Tables 12) It is interesting to indicate that NO2 (para red) derivative has been synthesized

and characterized several years ago35 Regarding the CH3 substitution the obtained isomers

lie almost at the same energy with small deviation for the ortho(C12)-CH3 isomer which was

found above the more stable meta and para isomers by 38 kcalmol and 33 kcalmol than the

ortho-CH3(C16) one This weak instability arises from the presence of interactions between

CH3 and the azo group revealing an average positive overlap population for the N-H(CH3)

contacts However the meta isomer is disfavored by the enthalpy and the Gibbs free energy

(∆H = 82 and ∆G = 94 kcalmol) The obtained DFT results match well with the combined

X-ray and NMR analysis on phenyl substituted suggesting that electron-withdrawing

substituent like NO225 and Cl36 stabilize the hydrazo form at para position Mulliken

population analysis has been provided in order to evaluate electron-donating or electron-

withdrawing effects of the used substitions at the para position The attached substituent is

connected to the phenyl ring through C(14) carbon atom where its net charge endure

modifications in accordance with the electron-donating or electron-withdrawing Indeed

Mulliken atomic net charges are used to estimate atomic charges and since these values

evaluate the electronic effects of different substituents A consistent trend can be seen in

Table 1 from the values collected using B3LYP method for para substitution The comparison

is based on the atomic net charges of the C(14) carbon atom before (+0 101) and after

substitution One can observe the decreasing of positive charge on C(14) atom in the order of

NO2 (+0140) gt CF3 (+0129) gt Cl (+0113) gt NH2 (+0080) gt CH3 (+0050) emphasizing the

electron-withdrawing effect increasing from CH3 to NO2 It can be seen from the Table 1 that

NO2 has the strongest electron-withdrawing effect which significantly decreases the

electronegativity of C(14) while the CH3 has the strongest electron-donating effect which

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

Page 18 of 26C

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

Page 19 of 26C

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

Page 20 of 26C

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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Page 24 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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interatomic distance observed in neutral NndashH bond

The 1-phenylazo-2-naphthol is the purpose of this study is among the azo species

which has been theoretically and experimentally investigated and widely used as well as its

derivatives19 Still there is no comprehensive overview on their electronic structure

properties and substitution effects so far This is what we endeavor to show in this paper

through a theoretical study provided by means of DFT HF and TD-DFT methods All the

optimized geometries have been carried out using the HF and B3LYP functional which has

been shown to reproduce efficiently the experimental structure but the results always remain

depending on the level of theory and the used basis set

Results and discussion

Geometry optimization

Unsubstituted species

The full geometry optimizations were carried out on the hydrazo and azo forms of 1-

phenylazo-2-naphthol in gas phase The obtained structures are displayed in Fig 1 with

atom-numbering shown in Scheme 1 (a and b) while the geometrical and energetic

parameters are gathered in Tables 1-3 The 1-phenylazo-2-naphthol in its hydrazo form has

been structurally characterized by X-ray diffraction since more than three decades24-26

The obtained results demonstrate a small energy difference between both structures a

and b of 18 and 08 kcalmol in favour of the hydrazo form obtained by B3LYP and HF

methods respectively using the same basis set for better description (See computational

details) These results are comparable to previously carried out theoretical studies using AM1

and ab initio calculations and exhibiting large HOMO-LUMO gaps of 302 and 319 eV

respectively27 as shown in Fig 2 Thus confirming the tautomers interconverting in solution

The thermodynamic measure of molecular stability is H which gives the enthalpy of the

compound relative to the reference state of its constituent elements under standard conditions

The thermodynamic data obtained by our DFT calculations provide an opportunity to

establish a stability order between different isomers as displayed in Fig 1 Indeed the ∆H

has the meaning of energy difference between the two OndashHbullbullbullN and NndashHbullbullbullO ground-state

vibrational levels corroborating the stability order discussed above concerning the trend of the

total bonding energy (TBE) The migration of the proton between the oxygen and the nitrogen

atoms in the azo and the hydrazo forms respectively does not require an important energy

barrier as shown in Scheme 2 where the transition state is separated from the azo and

hydrazone forms only by 04 and 22 kcalmol respectively Accordingly when the

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geometries of the azo hydrazo and transition state are compared one can see the reduction of

the NbullbullbullO distance of the transition state of 2463 Aring with regard to the initial and the final

forms of 2645 and 2718 Aring (B3LYP) respectively For the transition state the ObullbullbullH and

HbullbullbullN distances become 1207 and 1256 Aring respectively as compared to initial azo form

values of 1006 and 1639 Aring and those of the final hydrazone form of 1683 and 1035 Aring

respectively The predominance of the hydrazo form has been suggested by many previous

studies using X-ray photoelectron spectroscopy and diffuse reflectance of the solids2829 The

occurring migration affects scarcely the phenyl ring where a delocalized scheme is present in

both forms but one naphthylrsquos ring of the hydrazo form undergoes significant changes

displaying a clear localized scheme with long C1-C6 and C5-C6 and short C4-C5 bond lengths

of 1470 1448 and 1350 Aring respectively while a localized scheme is present in both

naphthyl rings for the azo form as displayed by the average C-C bond distance gathered in

Tables 12 It is worthwhile indicating that the hydrogen migration gives rise to noticeable

structural variations in the vicinity of the azo group for the hydrazo form which can be

evidenced by the bond lengths of N1-N2 (1300 Aring) C11-N2 (1397 Aring) C2-N1 (1323 Aring) N2-H

(1035 Aring) C-O (1256 Aring) and ObullbullbullH interaction of 1683 Aring compared to those obtained for

the azo form given by the following bond distances N1-N2 (1268 Aring) C11-N2 (1409 Aring) C2-

N1 (1379 Aring) O-H (1006 Aring) C-O (1336 Aring) and N2bullbullbullH interaction of 1639 Aring Generally for

the azo form the N-N double bond length is 1250 Aring3031 slightly shorter than that found by

our calculations Itrsquos noticeable that in the azo form the aromatic phenyl and the naphthyl

rings are oriented to each other by (θ = 200deg) whereas they are coplanar in the hydrazo form

(θ = 10deg) where θ is the C3C2C11C16 dihedral angle The twist in the azo form can be likely

explained by the weak delocalization over the C11-N2 (1409 Aring) and C2-N1 (1379 Aring) bonds

However the flatness of the hydrazo form helps the extension of the delocalization of the

system It is worth noting that the calculated geometrical parameters are comparable to those

observed experimentally in previous works2425

The HF results do not show severe discrepancies with regard to those obtained by the

DFTB3LYP method In general the geometrical parameters gathered in Tables 12 display

similarities between B3LYP and HF but the largest discrepancy is calculated for the N=N

bond distance in the azo form which deviates by 005 Aring (1219 Aring) than that obtained by

B3LYP (1268 Aring) The energetic data show also the same tendency to that obtained by

B3LYP but with reduced relative energy values as clearly displayed in Fig 2 and Tables 3

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It can be said that the formation of the intramolecular NminusHbullbullbullO hydrogen bond should

contribute to stabilize slightly the hydrazo form in agreement with previous experimental

results3233

Substitution effects

For this purpose we will be interested in this part in giving a deeper insight to the role

likely to be played by the various substituents (CH3 CF3 NH2 Cl and NO2) used according to

their electronic properties because azo dyes can be easily prepared with a wide range of

donor and acceptor groups

We analyze by means of the density functional theory (DFT) and HF calculations all

possible predicted isomers carried out on the hydrazo form The different isomers are

obtained alternately by substitution on the carbon sites belonging to the phenyl ring namely

C12 and C16 (ortho) C13 and C15 (meta) and C14 (para) atoms positions (Fig 3) respectively in

order to evaluate the electron donating and accepting abilities of each used substituent and to

establish a stability order for each substitution

One can observe that the bond lengths vary slightly from one isomer to other for each

substitution The different substituents provoke shortening or lengthening of the bond

distances in accordance with either the electron-withdrawing or the electron-donating

characters respectively The findings displayed in Fig 3 show clearly that the ortho(C12)

position is the less favored in all cases giving rise to isomers which are less stable than their

analogs ortho(C16) meta and para ones It is worth to mention that the meta(C15) isomers are

not discussed in this work because of their similarities of those obtained for meta(C13) ones

thus we contented only with presenting the results of the latter On the other hand these

results highlight a hard competition between para and meta isomers except for the NH2 For

the chlorine substitution the para-Cl isomer lies at the same energy than the meta-Cl one

The latter isomer was recently synthesized and characterized by X-ray diffraction revealing a

comparative geometrical parameters than our theoretical findings34 However the ortho(C12)-

Cl isomer is less stable by 74 kcalmol than the para-Cl and meta-Cl ones but the ortho(C16)-

Cl isomer is more stable than its analogous substituted on C16 position by 48 kcalmol

stabilized by NndashHbullbullbullCl interactions It is worth noting that the calculated bond distances

within the phenyl ring for the para-Cl isomer are somewhat shortened compared to those of

the unsubstituted hydrazo form evidenced by the average C-C bond distances as displayed in

Tables 12 This reports the predicted structure parameters and the available experimental

data inversely to the withdrawing property of chlorine the N-N and C-N bonds are not

Page 6 of 26C

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affected The less stable ortho(C12)-Cl isomer exhibits a distorted structure with a dihedral

C3C2C11C16 angle of 444deg Indeed this twisted geometry stemmes essentially from strong

repulsions between the azo group and the chlorine atom whose the average Cl-N2 overlap

population is evaluated as negative value of -0056 (Fig 3) despite of the long distance of

3045 Aring Contrarily to the other substitutions there is no competition between para-NH2 and

meta-NH2 where the former isomer is more stable than the latter one by 101 kcalmol So

the following stability order is established para-NH2 gt ortho(C15)-NH2 gt meta-NH2 gt

ortho(C12)-NH2 Surprisingly NH2 as donor substituent is expected to decrease bond

distances within the attached phenyl ring however slight lengthening for these bond

distances are calculated as displayed in Tables 12 thereby the electron density on the

aromatic ring is reduced For the NO2 CF3 and CH3 no noticeable variations are emphasized

(Tables 12) It is interesting to indicate that NO2 (para red) derivative has been synthesized

and characterized several years ago35 Regarding the CH3 substitution the obtained isomers

lie almost at the same energy with small deviation for the ortho(C12)-CH3 isomer which was

found above the more stable meta and para isomers by 38 kcalmol and 33 kcalmol than the

ortho-CH3(C16) one This weak instability arises from the presence of interactions between

CH3 and the azo group revealing an average positive overlap population for the N-H(CH3)

contacts However the meta isomer is disfavored by the enthalpy and the Gibbs free energy

(∆H = 82 and ∆G = 94 kcalmol) The obtained DFT results match well with the combined

X-ray and NMR analysis on phenyl substituted suggesting that electron-withdrawing

substituent like NO225 and Cl36 stabilize the hydrazo form at para position Mulliken

population analysis has been provided in order to evaluate electron-donating or electron-

withdrawing effects of the used substitions at the para position The attached substituent is

connected to the phenyl ring through C(14) carbon atom where its net charge endure

modifications in accordance with the electron-donating or electron-withdrawing Indeed

Mulliken atomic net charges are used to estimate atomic charges and since these values

evaluate the electronic effects of different substituents A consistent trend can be seen in

Table 1 from the values collected using B3LYP method for para substitution The comparison

is based on the atomic net charges of the C(14) carbon atom before (+0 101) and after

substitution One can observe the decreasing of positive charge on C(14) atom in the order of

NO2 (+0140) gt CF3 (+0129) gt Cl (+0113) gt NH2 (+0080) gt CH3 (+0050) emphasizing the

electron-withdrawing effect increasing from CH3 to NO2 It can be seen from the Table 1 that

NO2 has the strongest electron-withdrawing effect which significantly decreases the

electronegativity of C(14) while the CH3 has the strongest electron-donating effect which

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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rd

(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

Page 17 of 26C

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18

Page 18 of 26C

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

Page 19 of 26C

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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Page 24 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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geometries of the azo hydrazo and transition state are compared one can see the reduction of

the NbullbullbullO distance of the transition state of 2463 Aring with regard to the initial and the final

forms of 2645 and 2718 Aring (B3LYP) respectively For the transition state the ObullbullbullH and

HbullbullbullN distances become 1207 and 1256 Aring respectively as compared to initial azo form

values of 1006 and 1639 Aring and those of the final hydrazone form of 1683 and 1035 Aring

respectively The predominance of the hydrazo form has been suggested by many previous

studies using X-ray photoelectron spectroscopy and diffuse reflectance of the solids2829 The

occurring migration affects scarcely the phenyl ring where a delocalized scheme is present in

both forms but one naphthylrsquos ring of the hydrazo form undergoes significant changes

displaying a clear localized scheme with long C1-C6 and C5-C6 and short C4-C5 bond lengths

of 1470 1448 and 1350 Aring respectively while a localized scheme is present in both

naphthyl rings for the azo form as displayed by the average C-C bond distance gathered in

Tables 12 It is worthwhile indicating that the hydrogen migration gives rise to noticeable

structural variations in the vicinity of the azo group for the hydrazo form which can be

evidenced by the bond lengths of N1-N2 (1300 Aring) C11-N2 (1397 Aring) C2-N1 (1323 Aring) N2-H

(1035 Aring) C-O (1256 Aring) and ObullbullbullH interaction of 1683 Aring compared to those obtained for

the azo form given by the following bond distances N1-N2 (1268 Aring) C11-N2 (1409 Aring) C2-

N1 (1379 Aring) O-H (1006 Aring) C-O (1336 Aring) and N2bullbullbullH interaction of 1639 Aring Generally for

the azo form the N-N double bond length is 1250 Aring3031 slightly shorter than that found by

our calculations Itrsquos noticeable that in the azo form the aromatic phenyl and the naphthyl

rings are oriented to each other by (θ = 200deg) whereas they are coplanar in the hydrazo form

(θ = 10deg) where θ is the C3C2C11C16 dihedral angle The twist in the azo form can be likely

explained by the weak delocalization over the C11-N2 (1409 Aring) and C2-N1 (1379 Aring) bonds

However the flatness of the hydrazo form helps the extension of the delocalization of the

system It is worth noting that the calculated geometrical parameters are comparable to those

observed experimentally in previous works2425

The HF results do not show severe discrepancies with regard to those obtained by the

DFTB3LYP method In general the geometrical parameters gathered in Tables 12 display

similarities between B3LYP and HF but the largest discrepancy is calculated for the N=N

bond distance in the azo form which deviates by 005 Aring (1219 Aring) than that obtained by

B3LYP (1268 Aring) The energetic data show also the same tendency to that obtained by

B3LYP but with reduced relative energy values as clearly displayed in Fig 2 and Tables 3

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It can be said that the formation of the intramolecular NminusHbullbullbullO hydrogen bond should

contribute to stabilize slightly the hydrazo form in agreement with previous experimental

results3233

Substitution effects

For this purpose we will be interested in this part in giving a deeper insight to the role

likely to be played by the various substituents (CH3 CF3 NH2 Cl and NO2) used according to

their electronic properties because azo dyes can be easily prepared with a wide range of

donor and acceptor groups

We analyze by means of the density functional theory (DFT) and HF calculations all

possible predicted isomers carried out on the hydrazo form The different isomers are

obtained alternately by substitution on the carbon sites belonging to the phenyl ring namely

C12 and C16 (ortho) C13 and C15 (meta) and C14 (para) atoms positions (Fig 3) respectively in

order to evaluate the electron donating and accepting abilities of each used substituent and to

establish a stability order for each substitution

One can observe that the bond lengths vary slightly from one isomer to other for each

substitution The different substituents provoke shortening or lengthening of the bond

distances in accordance with either the electron-withdrawing or the electron-donating

characters respectively The findings displayed in Fig 3 show clearly that the ortho(C12)

position is the less favored in all cases giving rise to isomers which are less stable than their

analogs ortho(C16) meta and para ones It is worth to mention that the meta(C15) isomers are

not discussed in this work because of their similarities of those obtained for meta(C13) ones

thus we contented only with presenting the results of the latter On the other hand these

results highlight a hard competition between para and meta isomers except for the NH2 For

the chlorine substitution the para-Cl isomer lies at the same energy than the meta-Cl one

The latter isomer was recently synthesized and characterized by X-ray diffraction revealing a

comparative geometrical parameters than our theoretical findings34 However the ortho(C12)-

Cl isomer is less stable by 74 kcalmol than the para-Cl and meta-Cl ones but the ortho(C16)-

Cl isomer is more stable than its analogous substituted on C16 position by 48 kcalmol

stabilized by NndashHbullbullbullCl interactions It is worth noting that the calculated bond distances

within the phenyl ring for the para-Cl isomer are somewhat shortened compared to those of

the unsubstituted hydrazo form evidenced by the average C-C bond distances as displayed in

Tables 12 This reports the predicted structure parameters and the available experimental

data inversely to the withdrawing property of chlorine the N-N and C-N bonds are not

Page 6 of 26C

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affected The less stable ortho(C12)-Cl isomer exhibits a distorted structure with a dihedral

C3C2C11C16 angle of 444deg Indeed this twisted geometry stemmes essentially from strong

repulsions between the azo group and the chlorine atom whose the average Cl-N2 overlap

population is evaluated as negative value of -0056 (Fig 3) despite of the long distance of

3045 Aring Contrarily to the other substitutions there is no competition between para-NH2 and

meta-NH2 where the former isomer is more stable than the latter one by 101 kcalmol So

the following stability order is established para-NH2 gt ortho(C15)-NH2 gt meta-NH2 gt

ortho(C12)-NH2 Surprisingly NH2 as donor substituent is expected to decrease bond

distances within the attached phenyl ring however slight lengthening for these bond

distances are calculated as displayed in Tables 12 thereby the electron density on the

aromatic ring is reduced For the NO2 CF3 and CH3 no noticeable variations are emphasized

(Tables 12) It is interesting to indicate that NO2 (para red) derivative has been synthesized

and characterized several years ago35 Regarding the CH3 substitution the obtained isomers

lie almost at the same energy with small deviation for the ortho(C12)-CH3 isomer which was

found above the more stable meta and para isomers by 38 kcalmol and 33 kcalmol than the

ortho-CH3(C16) one This weak instability arises from the presence of interactions between

CH3 and the azo group revealing an average positive overlap population for the N-H(CH3)

contacts However the meta isomer is disfavored by the enthalpy and the Gibbs free energy

(∆H = 82 and ∆G = 94 kcalmol) The obtained DFT results match well with the combined

X-ray and NMR analysis on phenyl substituted suggesting that electron-withdrawing

substituent like NO225 and Cl36 stabilize the hydrazo form at para position Mulliken

population analysis has been provided in order to evaluate electron-donating or electron-

withdrawing effects of the used substitions at the para position The attached substituent is

connected to the phenyl ring through C(14) carbon atom where its net charge endure

modifications in accordance with the electron-donating or electron-withdrawing Indeed

Mulliken atomic net charges are used to estimate atomic charges and since these values

evaluate the electronic effects of different substituents A consistent trend can be seen in

Table 1 from the values collected using B3LYP method for para substitution The comparison

is based on the atomic net charges of the C(14) carbon atom before (+0 101) and after

substitution One can observe the decreasing of positive charge on C(14) atom in the order of

NO2 (+0140) gt CF3 (+0129) gt Cl (+0113) gt NH2 (+0080) gt CH3 (+0050) emphasizing the

electron-withdrawing effect increasing from CH3 to NO2 It can be seen from the Table 1 that

NO2 has the strongest electron-withdrawing effect which significantly decreases the

electronegativity of C(14) while the CH3 has the strongest electron-donating effect which

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

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Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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It can be said that the formation of the intramolecular NminusHbullbullbullO hydrogen bond should

contribute to stabilize slightly the hydrazo form in agreement with previous experimental

results3233

Substitution effects

For this purpose we will be interested in this part in giving a deeper insight to the role

likely to be played by the various substituents (CH3 CF3 NH2 Cl and NO2) used according to

their electronic properties because azo dyes can be easily prepared with a wide range of

donor and acceptor groups

We analyze by means of the density functional theory (DFT) and HF calculations all

possible predicted isomers carried out on the hydrazo form The different isomers are

obtained alternately by substitution on the carbon sites belonging to the phenyl ring namely

C12 and C16 (ortho) C13 and C15 (meta) and C14 (para) atoms positions (Fig 3) respectively in

order to evaluate the electron donating and accepting abilities of each used substituent and to

establish a stability order for each substitution

One can observe that the bond lengths vary slightly from one isomer to other for each

substitution The different substituents provoke shortening or lengthening of the bond

distances in accordance with either the electron-withdrawing or the electron-donating

characters respectively The findings displayed in Fig 3 show clearly that the ortho(C12)

position is the less favored in all cases giving rise to isomers which are less stable than their

analogs ortho(C16) meta and para ones It is worth to mention that the meta(C15) isomers are

not discussed in this work because of their similarities of those obtained for meta(C13) ones

thus we contented only with presenting the results of the latter On the other hand these

results highlight a hard competition between para and meta isomers except for the NH2 For

the chlorine substitution the para-Cl isomer lies at the same energy than the meta-Cl one

The latter isomer was recently synthesized and characterized by X-ray diffraction revealing a

comparative geometrical parameters than our theoretical findings34 However the ortho(C12)-

Cl isomer is less stable by 74 kcalmol than the para-Cl and meta-Cl ones but the ortho(C16)-

Cl isomer is more stable than its analogous substituted on C16 position by 48 kcalmol

stabilized by NndashHbullbullbullCl interactions It is worth noting that the calculated bond distances

within the phenyl ring for the para-Cl isomer are somewhat shortened compared to those of

the unsubstituted hydrazo form evidenced by the average C-C bond distances as displayed in

Tables 12 This reports the predicted structure parameters and the available experimental

data inversely to the withdrawing property of chlorine the N-N and C-N bonds are not

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affected The less stable ortho(C12)-Cl isomer exhibits a distorted structure with a dihedral

C3C2C11C16 angle of 444deg Indeed this twisted geometry stemmes essentially from strong

repulsions between the azo group and the chlorine atom whose the average Cl-N2 overlap

population is evaluated as negative value of -0056 (Fig 3) despite of the long distance of

3045 Aring Contrarily to the other substitutions there is no competition between para-NH2 and

meta-NH2 where the former isomer is more stable than the latter one by 101 kcalmol So

the following stability order is established para-NH2 gt ortho(C15)-NH2 gt meta-NH2 gt

ortho(C12)-NH2 Surprisingly NH2 as donor substituent is expected to decrease bond

distances within the attached phenyl ring however slight lengthening for these bond

distances are calculated as displayed in Tables 12 thereby the electron density on the

aromatic ring is reduced For the NO2 CF3 and CH3 no noticeable variations are emphasized

(Tables 12) It is interesting to indicate that NO2 (para red) derivative has been synthesized

and characterized several years ago35 Regarding the CH3 substitution the obtained isomers

lie almost at the same energy with small deviation for the ortho(C12)-CH3 isomer which was

found above the more stable meta and para isomers by 38 kcalmol and 33 kcalmol than the

ortho-CH3(C16) one This weak instability arises from the presence of interactions between

CH3 and the azo group revealing an average positive overlap population for the N-H(CH3)

contacts However the meta isomer is disfavored by the enthalpy and the Gibbs free energy

(∆H = 82 and ∆G = 94 kcalmol) The obtained DFT results match well with the combined

X-ray and NMR analysis on phenyl substituted suggesting that electron-withdrawing

substituent like NO225 and Cl36 stabilize the hydrazo form at para position Mulliken

population analysis has been provided in order to evaluate electron-donating or electron-

withdrawing effects of the used substitions at the para position The attached substituent is

connected to the phenyl ring through C(14) carbon atom where its net charge endure

modifications in accordance with the electron-donating or electron-withdrawing Indeed

Mulliken atomic net charges are used to estimate atomic charges and since these values

evaluate the electronic effects of different substituents A consistent trend can be seen in

Table 1 from the values collected using B3LYP method for para substitution The comparison

is based on the atomic net charges of the C(14) carbon atom before (+0 101) and after

substitution One can observe the decreasing of positive charge on C(14) atom in the order of

NO2 (+0140) gt CF3 (+0129) gt Cl (+0113) gt NH2 (+0080) gt CH3 (+0050) emphasizing the

electron-withdrawing effect increasing from CH3 to NO2 It can be seen from the Table 1 that

NO2 has the strongest electron-withdrawing effect which significantly decreases the

electronegativity of C(14) while the CH3 has the strongest electron-donating effect which

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

02

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

02

04

06

08

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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affected The less stable ortho(C12)-Cl isomer exhibits a distorted structure with a dihedral

C3C2C11C16 angle of 444deg Indeed this twisted geometry stemmes essentially from strong

repulsions between the azo group and the chlorine atom whose the average Cl-N2 overlap

population is evaluated as negative value of -0056 (Fig 3) despite of the long distance of

3045 Aring Contrarily to the other substitutions there is no competition between para-NH2 and

meta-NH2 where the former isomer is more stable than the latter one by 101 kcalmol So

the following stability order is established para-NH2 gt ortho(C15)-NH2 gt meta-NH2 gt

ortho(C12)-NH2 Surprisingly NH2 as donor substituent is expected to decrease bond

distances within the attached phenyl ring however slight lengthening for these bond

distances are calculated as displayed in Tables 12 thereby the electron density on the

aromatic ring is reduced For the NO2 CF3 and CH3 no noticeable variations are emphasized

(Tables 12) It is interesting to indicate that NO2 (para red) derivative has been synthesized

and characterized several years ago35 Regarding the CH3 substitution the obtained isomers

lie almost at the same energy with small deviation for the ortho(C12)-CH3 isomer which was

found above the more stable meta and para isomers by 38 kcalmol and 33 kcalmol than the

ortho-CH3(C16) one This weak instability arises from the presence of interactions between

CH3 and the azo group revealing an average positive overlap population for the N-H(CH3)

contacts However the meta isomer is disfavored by the enthalpy and the Gibbs free energy

(∆H = 82 and ∆G = 94 kcalmol) The obtained DFT results match well with the combined

X-ray and NMR analysis on phenyl substituted suggesting that electron-withdrawing

substituent like NO225 and Cl36 stabilize the hydrazo form at para position Mulliken

population analysis has been provided in order to evaluate electron-donating or electron-

withdrawing effects of the used substitions at the para position The attached substituent is

connected to the phenyl ring through C(14) carbon atom where its net charge endure

modifications in accordance with the electron-donating or electron-withdrawing Indeed

Mulliken atomic net charges are used to estimate atomic charges and since these values

evaluate the electronic effects of different substituents A consistent trend can be seen in

Table 1 from the values collected using B3LYP method for para substitution The comparison

is based on the atomic net charges of the C(14) carbon atom before (+0 101) and after

substitution One can observe the decreasing of positive charge on C(14) atom in the order of

NO2 (+0140) gt CF3 (+0129) gt Cl (+0113) gt NH2 (+0080) gt CH3 (+0050) emphasizing the

electron-withdrawing effect increasing from CH3 to NO2 It can be seen from the Table 1 that

NO2 has the strongest electron-withdrawing effect which significantly decreases the

electronegativity of C(14) while the CH3 has the strongest electron-donating effect which

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

02

04

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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increases drastically the electronegativity of C(14)

In the light of these results the geometry of the ortho(C12) isomers distortion

decreases following the order Cl gt NO2 gt CF3 gt NH2 gt CH3 In terms of donor effects the

methyl group induces the smallest angle between the phenyl and the naphtyl rings in the

isolated molecule The energetic data obtained by HF method show the same tendencies to

those of B3LYP confirming the hard competition between para and meta substitutions while

the ortho-(C12) position remains the less favorable but show in fact relatively reduced relative

energies as clearly displayed in Fig 2 and Tables 3 As can be seen from Tables 12 the

proton position is strongly shifted toward the oxygen in NH2 case with regard to the other

substituted species where HO distances can be classified following the increasing order

NH2 lt Cl lt CH3 lt NO2 lt CF3 The different calculations performed on the substituted azo

form provide isomers slightly less stable than those of their homologous of hydrazo ones of

each considered position thus the theoretical results in the range of 1-25 kcalmol or slightly

higher can be considered as correct description of the tautomeric equilibrium of the

substituted species For this reason the different substitutions of the hydrazo form have been

the focus of our theoretical study rather than those of the azo form ones

Electronic spectra

The properties of the ndashN=Nndash group have been particularly investigated by UV-Vis

spectroscopy where various theoretical and experimental results have been reported37-40 The

theoretical electronic spectra of the various compounds investigated in this study were

calculated by the time-dependent density functional theory (TD-DFT) method using B3LYP

functional firstly in gas phase and secondly in three different solvents hexane (non polar)

ethanol (polar protic) and (DMSO polar aprotic) Recently a variety of computational

methods have been investigated for calculating UV-Vis spectra by means of the framework of

TD-DFT41-42 Previous theoretical works have shown that B3LYP produces relatively good

results when compared to the experimental available data39 Furthermore the including of

solvation model into the calculations generally improved the results when compared with the

experimental values44

The identification of the nature of different electronic transitions is based on the analysis of

the molecular orbital localization and their coefficients Our theoretical calculations allowed

us to clearly identify the spectral shape and position of such transitions

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

Page 14 of 26C

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n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

Page 15 of 26C

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rd

(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

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06

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

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02

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

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02

04

06

08

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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Electronic spectra of the unsubstituted species

The main band of the hydrazo form ranging from 425 to 450 nm centered at 439 nm

displays one maximum of wavelength and corresponding only to one electron transition

established between the HOMO and the LUMO (65ararr66a 98) with moderate oscillator

strength of 0470 relative to the visible absorption maxima as shown in Fig 4 This band is

due to the electronic transition of the π system of the phenyl and naphthyl rings the lone pair

of the nitrogen atom and the π system of the azo group and πC-O (transition of

nrarrπlowast and πrarrπ type) as sketched on Fig 2 Whereas the main band for the azo form lies at

421 nm is composed by three electronic transitions predominated by the HOMO to LUMO

(65ararr66a 82) followed by the HOMO-2 to LUMO (63ararr66a 15) and finally by the

weak transition from the HOMO-1 to the LUMO (64ararr66a 2) This band was due to the

electronic transition of the naphthyl ring phenyl ring and azo group (transition of πndashπ type)

as shown in Fig 2

The deviation of 18 nm between the main peaks of the hydrazo and azo forms (Fig 4) is due

to the difference in localization and contributions of the MOs involved in the transitions

However the different peaks are more shifted toward the high wavelength in various solvents

for the hydrazo form than those of the azo one Indeed the same tendencies can be observed

where the position of the main band (439 nm) undergoes red shift according to the solvent

polarity (27 nm) in hexane and (61 nm) in ethanol and DMSO For the hydrazo form the

main peak centred at 500 nm in ethanol solvent matches well with that obtained

experimentally45 while that of azo form (468 nm) deviates from the experimental one (429

nm) Surprisingly the weak band found at 248 nm calculated in gas phase (018) is strongly

affected in polar solvents showing a calculated large oscillator strength (098) which

corresponds only to the πrarrπ electronic transition of the naphtyl ring As said earlier the

energy gap between the LUMO and HOMO orbitals for the hydrazo form is relatively smaller

than the corresponding value in the azo form indicating that the electron transfer of the

HOMO to the first excited state LUMO is easier in the hydrazo form in agreement with a

small ∆E gap of 302 eV compared to that obtained of the azo form of 319 eV Therefore the

hydrazo form absorbs light at relatively high wavelengths in comparison with the azo one

This trend is also observed for the different electronic transitions calculated in the different

used solvents as gathered in Table 4 this indicates better molecular orbital overlap between

ground state and excited state

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

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08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

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Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Wavelength (nm)

Gas phase

DMSO

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Hexane

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00

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10

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Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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Electronic spectra of the substituted species

The Electronic spectra of the substituted species in gas phase (Fig 5) show that the

effects of the Cl NO2 and NH2 substitutions are comparable regarding the bathochrom shifts

of 19 17 and 33 nm respectively compared to those of the unsubstituted ones in agreement

with the weak ∆E diminution Also these substitutions are marked by the increasing of the

oscillator strength values as displayed in Table 4 Thereby this can be explained by the

substitution MOs participation in the main electronic transitions with variable contributions

The methyl substitution in gas phase does not provoke any changes of the electronic spectra

of the unsubstituted species compared to those of Cl NO2 and NH2 ones consistent with a

neglected variation of ∆E (300 vs 302 eV) and the weak diminution of the oscillator strength

(0500 vs 0470 au) In contrast the trifluoromethyl substituent leads to a slight blue shift (6

nm) in accordance with the weak ∆E difference (305 vs 302 eV) and the oscillator strength

growth (0417 vs 0470 au)

For the para-Cl para-NH2 and para-NO2 substitutions the electronic spectra obtained

in different solvents show bathochrom shifts of the main band compared to their

corresponding ones obtained in gas phase with important red shifts while those obtained for

CH3 and CF3 substitutions in the same solvents are less shifted by 23 nm in hexane 41 in

ethanol and 38 nm in DMSO Thereby the red shift increases according to the following

trend CF3 lt CH3 lt Cl lt NO2 lt NH2 Really the displacements provoked by the polar

solvents are more significant than that of the non-polar one as sketched in Fig 5 Indeed in

ethanol and DMSO solvents the main peaks of para-NO2 and para-NH2 are found to be

shifted by about 36 and 75 nm respectively compared to those for the unsubstituted hydrazo

species however these shifts are most important compared to those obtained in gas phase as

displayed in Fig 5

The different spectra stemming from Cl NH2 and NO2 substitutions in DMSO and

ethanol solvents are indistinguishable in positions the differences arise from the very small

deviation of the oscillator strength values which does not exceed 0014 au while those

obtained for CH3 and CF3 substitutions in the same solvents exhibit some differences

particularly the band situated at high energy (250 nm)

It is apparent that varying the substituents in (NH) compound has significant influence

on the electronic spectra except of the CH3 and CF3 substitutions where obvious differences

are emphasized by comparing the substituted and unsubstituted electronic spectra featured in

Fig 4 and Fig 5 respectively

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

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rd

(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

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08

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

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Wavelength (nm)

Gas phase

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Hexane

300 400 500 600

00

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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The electronic spectra of the para-Cl and para-NH2 are quite similar in shape while

the major differences reside in the reduction of the peak intensity appearing at 250 nm

displaying less intense peaks for the para-NH2 in DMSO and ethanol however its weakness

is more pronounced in hexane solvent For the para-NO2 one can observe the disappearance

of the peak at low wavelength inversely the peak centered at 536 keeps comparable

intensities than those obtained for the para-NH2 and in a lesser degree than those found for

the para-Cl As can be seen from the Table 4 the different substitutions at para position of

the phenyl ring reduce the energy gaps consequently leads to absorption at relatively long

wavelengths as displayed by the different electronic spectra

For the para-CH3 the peak found at 250 nm obtained in DMSO is comparable to those

for the para-Cl and para-NH2 whereas the most important modification concerns the spectra

obtained in ethanol solvent where its intensity undergoes a strong reduction Really the

intensity of 250 nm band obtained in ethanol (026 au) decreases substantially compared to

that obtained in DMSO (095 au) as sketched in Fig 5

Computational details

DFT calculations were performed with the 201301 version of the Amsterdam Density

Functional (ADF) program46 developed by Baerends and co-workers47-51 All calculations

were carried out with the hybrid-type B3LYP functional (Beckersquos three parameter hybrid

exchange functional52 coupled with the Lee-Yang-Parr nonlocal correlation functional)53 and

ab initio HF method54 The standard ADF TZP basis set was used ie a triple-ζ Slater-type

orbital basis set for the valence shells augmented with single-ζ polarization functions (2p for

H 3d for C N F and Cl)4-51 Vibrational frequency calculation55-56 were performed on all the

optimized geometries to verify that these structures are characterized as true minima on the

potential energy surface Singlet-triplet excitation energies and the transition dipole lengths

were computed using TD-DFT as implemented in the Response57 code in the ADF package of

programs

The solvent effect using the Conductor-like Screening Model for realistic solvent (COSMO-

RS) developed by Klamt and coworkers58 was introduced in the single point DFT

calculations where the cartesian coordinates were extracted from the geometry optimizations

Representations of the molecular structures were done using the ADF-GUI42 and the

MOLEKEL4159 programs respectively

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

Page 14 of 26C

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rd

(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

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08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

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Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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Conclusion

DFT calculations in gas phase and in different solvents showed the preference of the

hydrazo form than the azo one which are also valuable in predicting the degree of electron-

delocalization for the hydrazo form The different calculations showed that the substitution

on the ortho(C12) position is the less sable while the substitution on the ortho(C16) position

give isomers which do not deviate enough from those of the most stable meta and para ones

The population analysis provided a better understanding for evaluating electron-donation or

electron-withdrawing for different used substituents On the basis of TD-DFT calculations

we were able to correlate the peak positions and the n-π or π-π electronic transition

characteristics All the azo dyes displayed two bands in their electronic spectra in various

organic solvents except for the para-NH2 For all studied species the main peaks in UV-vis

spectra are attributed to the HOMO-LUMO electronic transitions Thus both from the point

of view of substitution and solvent effects the electronic spectra of hydrazo form doesnrsquot

undergo noticeable modifications when substituted by the CH3 and CF3 in conformity with

the unchangeable geometrical parameters

On the basis of the obtained HOMO-LUMO gaps and the electronic spectra one can

observe the bathochromic shift towards the long wavelengths with diminution of the HOMO-

LUMO energy gaps thus the enhancement of the wavelengths pursues the following

sequence CF3 lt CH3 lt Cl lt NO2 lt NH2

The different substitutions at para position of the phenyl ring reduce the energy gaps

consequently leads to absorption at relatively long wavelengths Also the different used

solvents are for important stabilization of LUMOs and HOMOs energies The calculated ∆E

for the CF3 substitution in gas phase is not affected by the used solvents explaining the

unchanged electronic spectra However the ∆E for the CH3 substitution undergo slight

diminutions in accordance with weak red shifts obtained in different solvents

The calculated HOMO-LUMO energy gap for the NH2 species obtained in different solvents

correspond to the smallest energies compared to those calculated for the other substituted

species in the same corresponding solvents in accordance with the largest wavelengths

The aprotic (DMSO) and the protic (ethanol) polar solvents act similarly on the

unsubstituted and the substituted studied species apart the difference arises from the small

deviation of the oscillator strength values which does not exceed (0014 au)

The intense peak obtained at high energy is attributed to the π-π electronic transitions of the

naphtyl ring which does not imply the azo group

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

Page 14 of 26C

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rd

(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

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08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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Acknowledgments

This work was supported by the Algerian MESRS (Ministegravere de lrsquoEnseignement Supeacuterieur et

de la Recherche Scientifique) and the DGRSDT (Direction Geacuteneacuterale de la Recherche

scientificque et du Deacuteveloppement Technologique) BZ is grateful to Dr F Djemai for his

fruitful help

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

Page 14 of 26C

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dif

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rd

(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

Page 15 of 26C

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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References

(1) Nejati K Rezvani Z Massoumi B Dyes and Pigments 2007 75 653

(2) Peker E Serin S Synth React Inorg MetOrg Chem 2004 34 859

(3) Buncel E Rajagonal S Synth React J Org Chem 1989 34 798

(4) Riul A Dos Santos D S Wohnrath K Di Tommazo R Carvalho ACPLF

Fonseca F J Oliveira O N Taylor D M Mattoso L H C Langmuir 18 2002 239

(5) Wang G Hou L Gan F Phys Status Solidi A 1999 174 269

(6) Morley J O Hutchings M G Zyss J Ledoux I J Chem Soc Perkin Trans 2 1997

1139

(7) Bershtein I Y Ginzburg O Russ Chem Rev 1972 41 97

(8) Ojala W H Sudbeck E A Lu L K Richardison T I Lovrien R E Gleason W B

J Am Chem Soc 1996 118 2131

(9) Castro MCR Schellenberg P Belsley M Fonceca AMC Fernandes SSM

Raposo MMM Dyes and Pigments 2012 95 392

(10) Raposo MMM Castro MCR Fonceca AMC Schellenberg P BelsleyM

Tetrahedron 2011 67 5189

(11) Raposo MMM Castro MCR Belsley M Fonceca AMC Dyes and Pigments

2011 91 454

(12) Raposo MMM Fonceca AMC Castro MCR Belsley M Cardoso MFS

Carvalho LM Coelho PL Dyes and Pigments 2011 91 62

(13) Zollinger H Colour Chemistry Synthesis Properties and Application of Organic Dyes

and Pigments VCH Weinheim 1991 pp 45-68

(14) Ozen A S Doruker P Aviyente V J Phys Chem A 2007 111 13506

(15) Peng Q Gao K Cheng L Dyes and Pigments 2007 14 89

(16) Shawali AS Harb NMS Badahdah KO J Heterocycl Chem 1985 22 1397

(17) Snehalatha M Sekar N Jayakumar V S Joe I H Spectrochim Acta Part A 2008

69 82

(18) Yesodha S K Sadashiva Pillai C K Tsutsumi N Prog Polym Sci 2004 29 45

(19) Towns A D Dyes and Pigments 1999 42 3

(20) Kanis D R Ratner M A Marks T J Chem Rev 1994 94 195

(21) Joshi H Kamounah F S van der Zwan G Gooijer C Antonov L J Chem Soc

Perkin Trans 2 2001 2303

(22) Fabian W M F Antonov L Nedltcheva D Kamounah F S Taylor P J J Phys

Chem A 2004 108 7603

Page 14 of 26C

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rd

(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

Page 15 of 26C

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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00

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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(23) Kelemen J Dyes and Pigments 1981 2 73

(24) Salmeacuten R Malterud KE Pedersen BF Acta Chem Scand A 1988 42 493

(25) Olivieri AC Wilson RB Paul IC Curtin DY J Am Chem Soc 1989 111

5225

(26) Chong-Yang L Vincent L Allen JB Chem Mater 1997 9 943

(27) Antonov L Kawauchi S Satoh M Komyama J 1998 38 157

(28) Yoshida T Bull Chem Soc Jpn 1980 53 498

(29) Dehari C Matsunga Y Tani K Bull Chem Soc Jpn 1970 43 3404

(30) Biswas N Umapathy S J Phys Chem A 1997 101 5555

(31) Dos Santos H F De Oliveira L F C Dantas S O Santos P S De Almeida W B Int J

Quant Chem 2000 80 1076

(32) Reeves R Kaiser R J Org Chem 1970 35 3670

(33) Kaul B L Nair P M Rama Rao A V Venkataraman K Tetrahedron Letters 1966 32

3897

(34) Benosmane A Mili A Bouguerria H Bouchoul A Acta Cryst 2013 E69 o1021

(35) Kucharski S Janik R New J Chem 1999 23 765

(36) Whitaker A Z Kristallogr 1980 152 227

(37) Chiang W Y Laane J J Chem Phys 1994 100 8755

(38) Molina V Merchan M Roos B O J Phys Chem A 1997 101 3478

(39) Kwasniewski S P Deleuze M S Francois J P Int J Quant Chem 2000 80 672

(40) Kwasniewski S P Francois J P Deleuze M S Int J Quant Chem 2001 85 557

(41) Jacquemin D Perpegravete E A Ciofini I Adamo C Theo Chim Acta 2008 120 405

(42) Jacquemin D Preat J Perpegravete E A Vercauteren D P Andreacute J M Ciofini I

Adamo C Int J Quant Chem 2011 111 4224

(43) Guillaumont D Nakamaura S Dyes and pigments 2000 46 85

(44) Cramer C J Truhlar D G Chem Rev 1999 99 2161

(45) Antonov L Stoyanov S Stoyanova T Dyes and pigments 1995 27 133

(46) ADF201301 Version Theoretical Chemistry Vrije Universiteit Amsterdam The

Netherlands SCM

(47) Baerends E J Ellis D E Ros P Chem Phys 1973 2 41

(48) te Velde G Baerends E J J Comput Phys 1992 99 84

(49) Fonseca Guerra C Snijders J G te Velde G Baerends E J Theo Chim Acc

1998 99 391

(50) Bickelhaupt F M Baerends E J Rev Comput Chem 2000 15 1

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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18

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

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02

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10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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(51) te Velde G Bickelhaupt F M Fonseca Guerra C van Gisbergen S J A Baerends

E J Snijders JG Ziegler T J Comput Chem 2001 22 931

(52) Becke A D J Chem Phys 1993 98 5648

(53) Lee C Yang W Parr RG Phys Rev B 1998 37 785

(54) Slater J C Phys Rev 1951 81 385

(55) Fan L Ziegler T J Chem Phys 1992 96 9005

(56) Fan L Ziegler T J Chem Phys 1992 96 6937

(57) Runge E Gross EKU Phys Rev Lett 1984 52 997

(58) Klamt A Schuumluumlmann G J Chem Soc Perkin Trans 2 1993 799

(59) Fluumlkiger P Luumlthi H P Portmann S J Weber MOLEKEL Version 43win32

Swiss Center for Scientific Computing (CSCS) Switzerland 2000-2001

httpwwwcscschmolekel

Page 16 of 26C

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

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Page 18 of 26C

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

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Figure captions

Scheme 1 Chemical structure of 1-phenylazo-2-naphthol with the atoms labeling used

throughout this paper

Fig 1 Optimized molecular structures of hydrazo and azo forms of 1-phenylazo-2-naphtol

Relative energies ∆E1 and ∆E2 caluclated using B3LYP and HF methods (with ZPE

corrections) respectively and relative thermodynamic parameters ∆H and ∆G (B3LYP) are

obtained between the two forms (kcalmol) and θ the dihedral angle (deg) between the phenyl

and the naphtyl rings

Scheme 2 Potential energy profile for the azo-hydrazo tautomerism of 1-phenylazo-2-

naphtol Azo (a) form transition state (b) and hydrazo form (c)

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol

The MOs involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the

hydrazo and azo forms respectively) are plotted with contour values of plusmn006 (ebohr3)

Fig 3 Optimized molecular structures of ortho meta and para isomers obtained by various

substitutions on the hydrazo form of 1-phenylazo-2-naphtol Relative energies ∆E1 and ∆E2

obtained by B3LYP and HF methods (with ZPE corrections) respectively and relative

thermodynamic parameters ∆H and ∆G (B3LYP) are obtained between isomers (kcalmol)

and θ the dihedral angle (deg) between the phenyl and the naphtyl rings

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and

para-NO2 (e) species obtained in gas phase hexane ethanol and DMSO

Table captions

Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo

forms and the para substituted species of 1-phenylazo-2-naphtol

Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and

the para substituted species of 1-phenylazo-2-naphtol

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from

various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps (ELUMO ndash EHOMO) and wavelength

λmax values (nm) obtained in gas phase and different solvents Oscillator strength values are

given in parentheses (au)

Page 17 of 26C

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Page 18 of 26C

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

Page 19 of 26C

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

Page 20 of 26C

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

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Page 24 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

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18

Page 18 of 26C

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

Page 19 of 26C

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

Page 20 of 26C

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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reco

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

Page 23 of 26C

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Page 24 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

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Table 1 Geometrical parameters calculated by DFTB3LYP method for the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1409 1470 (1453)a 1469 1475 1472 1480 1472 C2-C3 1440 1461 (1461) 1460 1464 1462 1465 1465 C3-C4 1422 1413 (1416) 1414 1412 1413 1412 1421 C4-C5 1419 1418 (1443) 1438 1439 1438 1440 1443 C5-C6 1364 1350 (1345) 1350 1350 1350 1349 1357 C6-C1 1413 1448 (1451) 1448 1448 1448 1448 1454 C 3-C7 1411 1402 (1404) 1402 1401 1402 1401 1411 C7-C8 1375 1382 (1384) 1382 1383 1382 1383 1388 C8-C9 1407 1398 (1398) 1398 1397 1398 1397 1406 C9-C10 1372 1380 (1377) 1380 1380 1380 1381 1386 C10-C4 1412 1404 (1401) 1404 1403 1404 1403 1412 C1-O 1336 1256 (1267) 1256 1253 1255 1251 1263 O-H 1006 1683 1687 1700 1676 1689 1674 N2-H 1639 1035 1035 1033 1035 1033 1034 C2- N1 1379 1323 (1340) 1324 1317 1322 1316 1334 N1-N2 1268 1300 (1314) 1299 1306 1303 1310 1299 C11-N2 1409 1397 (1415) 1398 1394 1396 1388 1402 C11-C12 1400 1397 (1388) 1397 1399 1397 1400 1403 C12-C13 1383 1386 (1387) 1384 1381 1386 1382 1389 C13-C14 1395 1393 (1388) 1400 1396 1391 1392 1409 C14-C15 1391 1391 (1384) 1394 1390 1389 1391 1406 C15-C16 1388 1387 (1388) 1388 1387 1386 1381 1390 C16-C11 1396 1397 (1395) 1395 1396 1397 1402 1403 Average C-C of phenyl ring

1392 1392 (1389) 1393 1391 1391 1391 1400

Average C-C of naphtyl ringb

1411 1428 (1428) 1429 1431 1431 1433 1435

Mulliken net charges Phenyl ring +0673 +0657 +0640 +0763 +0750 +0784 +0623 C(14) +0107 +0101 0050 +0129 +0113 +0140 +0080

Page 19 of 26C

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

Page 20 of 26C

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

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∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

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Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

Page 23 of 26C

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Page 24 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

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300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

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Table 2 Geometrical parameters calculated by HF method or the hydrazo and azo forms and the para

substituted species of 1-phenylazo-2-naphtol

a Ref [20] b corresponding to the ring attached to the azo group

Azo Hydrazo para-CH3 para-CF3 para-Cl para-NO2 para-NH2

Bond distances (Aring) C1-C2 1379 1487 (1453)a 1482 1493 1490 1498 1476 C2-C3 1437 1479 (1461) 1477 1482 1479 1482 1475 C3-C4 1405 1396 (1416) 1396 1397 1395 1395 1395 C4-C5 1421 1459 (1443) 1459 1461 1460 1461 1457 C5-C6 1349 1328 (1345) 1329 1328 1328 1327 1329 C6-C1 1417 1468 (1451) 1466 1469 1466 1466 1467 C 3-C7 1420 1395 (1404) 1396 1393 1394 1393 1398 C7-C8 1359 1376 (1384) 1376 1377 1376 1377 1374 C8-C9 1411 1390 (1398) 1392 1391 1390 1390 1394 C9-C10 1357 1374 (1377) 1374 1377 1375 1375 1373 C10-C4 1417 1395 (1401) 1396 1394 1395 1395 1398 C1-O 1333 1212 (1267) 1214 1210 1211 1210 1215 O-H 0952 1858 1839 1856 1849 1835 1834 N2-H 1838 0995 0996 0995 0995 0996 0997 C2- N1 1402 1261 (1340) 1285 1277 1277 1275 1289 N1-N2 1219 1293 (1314) 1285 1299 1297 1304 1280 C11-N2 1421 1396 (1415) 1398 1390 1391 1383 1403 C11-C12 1392 1389 (1388) 1385 1389 1388 1392 1386 C12-C13 1378 1382 (1387) 1383 1383 1379 1377 1380 C13-C14 1389 1385 (1388) 1388 1385 1379 1383 1390 C14-C15 1380 1384 (1384) 1391 1392 1378 1383 1388 C15-C16 1386 1382 (1388) 1379 1375 1379 1375 1381 C16-C11 1382 1389 (1395) 1388 1394 1387 1393 1384 Average C-C of phenyl ring

1384 1385 (1389) 1385 1386 1391 1383 1384

Average C-C of naphtyl ringb

140 1436 (1428) 1434 1438 1431 1438 1433

Page 20 of 26C

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Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

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his

Just

-IN

man

uscr

ipt i

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cept

ed m

anus

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or to

cop

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and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

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his

Just

-IN

man

uscr

ipt i

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cept

ed m

anus

crip

t pri

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cop

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iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

Page 23 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

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cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Page 24 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

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his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

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t pri

or to

cop

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and

pag

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mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Table 3 Relative energies ∆E1 and ∆E2 (kcalmol) between isomers obtained by B3LYP and HF methods and

C2C1C11C16 dihedral angles (θdeg) calculated (B3LYP) for different isomers obtained from various substitutions

Table 4 HOMOs and LUMOs energies (eV) enegy gaps ∆E (ELUMO ndash EHOMO) and wavelength λmax values (nm)

obtained in gas phase and different solvents Oscillator strength values are given in parentheses (au)

CH3 CF3 Cl NO2 NH2

∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E1 ∆E2 θ ∆E2 ∆E2 θ

Ortho(C12) 38 40 40 81 74 41 74 69 44 108 132 44 115 61 16

Ortho(C16) 05 00 2 49 37 18 22 20 44 56 49 0 20 15 19

Meta 00 00 3 02 16 4 00 00 3 17 16 2 31 54 10

Para 00 00 1 00 00 2 00 00 2 00 00 1 00 00 4

Hydrazo Azo CH3 CF3 Cl NO2 NH2

ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO ELUMO EHOMO

Gas phase

∆E

λmax

-275 -577

302

439 (0470)

-264 -583

319

429 (0388)

-264 -564

300

438 (0500)

-305 -610

305

433 (0417)

-291 -589

298

458 (0540)

-329 -634

295

456 (0586)

-258 -533

277

472 (0622)

Hexane

∆E

λ max

-279 -586

302

466 (0599)

-268 -586

312

445 (0296)

-273 -569

296

461 (0665)

-301 -602

301

456 (0594)

-300 -587

287

485 (0678)

-333 -625

278

485 (0771)

-264 -536

268

506 (0764)

Ethanol

∆E

λ max

-287 -586

299

500 (0780)

-275 -595

320

468 (0730)

-283 -577

294

502 (0836)

-298 -601

304

494 (0772)

-300 -587

287

529 (0867)

-328 -613

275

536 (1027)

-277 -543

266

575 (0956)

DMSO

∆E

λ max

-289 -587

298

500 (0787)

-276 -592

316

475 (0744)

-284 -577

293

502 (0842)

-298 -601

304

494 (0779)

-300 -587

287

529 (0877)

-329 -613

274

536 (1033)

-278 -543

265

575 (0964)

Page 21 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

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his

Just

-IN

man

uscr

ipt i

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anus

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cop

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iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

Page 23 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

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cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Page 24 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

∆E1 = 00 ∆E2 = 00

∆H = 00 ∆G = 0

θ = 10

∆E1 = 18 ∆E2 = 08

∆H = 12 ∆G = 09

θ = 200

Page 22 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

Page 23 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Page 24 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

For

pers

onal

use

onl

y T

his

Just

-IN

man

uscr

ipt i

s th

e ac

cept

ed m

anus

crip

t pri

or to

cop

y ed

iting

and

pag

e co

mpo

sitio

n I

t may

dif

fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Fig 2 Simplified MO diagrams of hydrazo (a) and azo (b) forms of 1-phenylazo-2-naphthol The MOs

involved in the main electronic transitions (λ = 439 nm and λ = 421 nm for the hydrazo and azo forms

respectively) are plotted with contour values of plusmn006 (ebohr3)

-2

-1

-5

-6

-7

Rel

ativ

e En

ergy

(eV

)

LUMO LUMO

HOMO HOMO

(a) (b)

439 nm 421 nm

Page 23 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

y Sa

n Fr

anci

sco

(UC

SF)

on 1

210

14

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pers

onal

use

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his

Just

-IN

man

uscr

ipt i

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fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

Page 24 of 26C

an J

Che

m D

ownl

oade

d fr

om w

ww

nrc

rese

arch

pres

sco

m b

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n Fr

anci

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(UC

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on 1

210

14

For

pers

onal

use

onl

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his

Just

-IN

man

uscr

ipt i

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anus

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e co

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sitio

n I

t may

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fer

from

the

fina

l off

icia

l ver

sion

of

reco

rd

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

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300 400 500 600

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

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Page 24 of 26C

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Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

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Wavelength (nm)

Gas phase

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300 400 500 600

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02

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

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Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 4 Electronic spectra for the hydrazo (a) and azo (b) forms obtained in gas phase hexane ethanol and DMSO

(a) (b)

Page 25 of 26C

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300 400 500 600

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Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

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Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

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300 400 500 600

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Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

300 400 500 600

00

02

04

06

08

10

Oscillator strength (au)

Wavelength (nm)

Gas phase

DMSO

Ethanol

Hexane

Fig 5 Electronic spectra for the para-CF3 (a) para-NH2 (b) para-CH3 (c) para-Cl (d) and para-NO2 (e) species obtained in gas phase hexane ethanol and

DMSO

(a) (b)

(c) (d) (e)

Page 26 of 26C

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