Supporting Information

Meeting the Challenging Electronic Structure of

Thiophene-Based Heterophenoquinones

Francesco Tampieri, Letizia Colella, Ali Maghsoumi, Javier Martí-Rujas, Emilio Parisini,

Matteo Tommasini, Chiara Bertarelli, Antonio Barbon

I. Synthesis of QDTT S2

II. UV-visible characterization S3

III. Hyperfine coupling constants calculations for the monomer of QBT S4

IV. DFT calculations of vibrational properties S5

V. X-ray data collection S7

VI. 1H-NMR spectra of QBT S12

VII. EPR spectrum of QBT in chloroform S13

S2

I - Synthesis of QDTT

Unless otherwise specified, all reagents, catalysts, spectroscopic grade and reagent grade solvents

were commercial (Sigma Aldrich). All reactions of air- water-sensitive reagents and intermediates

were carried out in dried glassware and argon atmosphere. Solvents were previously dried by

conventional methods and stored under argon. Air- and water-sensitive solutions were transferred

with hypodermic syringes or via cannula.

4,4’-(Dithieno[3,2-b:2’,3’-d]thiophene-2,6-diyl)bis(2,6-di-tert-butylphenol) (ADTT)

Pd(PPh3)4 (82 mg, 0.0706 mmol), tris[3,5-di-tert-butylphenol-4-(trimethylsilyloxy)phenyl]boroxine

(644.5 mg, 0.706 mmol) and Na2CO3 (673 mg, 6.35 mmol) aq solution (1 M) were added to a solution

of 2,6-dibromodithieno[3,2-b:2`,3`-d]thiophene (250 mg, 0.706 mmol) in previously degassed DME

(2:1 with respect to water). The reaction was refluxed overnight, and then it was extracted with ethyl

acetate. The organic fractions were combined, dried over Na2SO4, filtered, and then the solvent was

removed under reduced pressure. The raw product was purified using flash chromatography (silica

gel, 95:5 hexane: ethyl acetate) to afford 175 mg (41% yield) of ADTT as a yellow crystalline solid.

1H-NMR (400 MHz, CDCl3, ppm): δ 7.454 (s, 4H; Ph-H), 7.355 (s, 2H; Dithienoth-H3,H5), 5.305 (s, 2H;

-OH), 1.505 (s, 36H; t-Bu); MS (ESI): m/z calcd for C36H44O2S3+H+: 605 [M+H+], found: 604.6 (M+).

4,4’-(dithieno[3,2-b:2’,3’-d]thiophene-2,6-di-yl)bis(2,6-di-tert-butylcyclohexa-2,5-dienone) (QDTT)

To a solution of ADTT (100 mg, 0.165 mmol) in CH2Cl2 (70 mL), K3Fe(CN)6 (543 mg, 1.65 mmol) and a

0.4 M aq. solution of KOH (925.8 mg, 16.5 mmol) were added. The resulting mixture was stirred until

the starting material was completely reacted (≈ 30 min). The reaction mixture was extracted with

methylene chloride and washed with water and the organic solvent was removed under reduced

pressure, giving the desired product in quantitative yield as a green solid.

1H-NMR (600 MHz, (CD3)2CO, ppm): δ 8.08 (s, 2H; Th1-H), 7.68 (s, 2H; Ph-H), 7.33 (s, 2H; Ph-H),

1.364 (s, 36H; t-Bu); MS (ESI): m/z calcd for C36H42O2S3+H+: 603 [M+H+], found: 603.6 (M+).

S3

II - UV-visible characterization

250 300 350 400 450 500

ADTT

ABTA

bso

rba

nce

(a

.u.)

Wavelength (nm)

Figure S1. Normalized UV-Vis absorption spectra in chloroform of the aromatic precursors: ADTT

(red line), ABT (green line).

500 550 600 650 700 750 800 850 900

QDTT

QBT

Wavelength (nm)

Ab

so

rba

nce

(a

.u.)

Figure S2. Normalized UV-Vis absorption spectra of quinones in chloroform: QDTT (red line), QBT

(green line).

S4

III - Hyperfine coupling constants calculations for the monomer of QBT

DFT calculations of the hyperfine coupling constants (hfccs) for the half molecule of QBT. The

calculations are done with Gaussian09 using the functional B3LYP and 6-311g** as basis set.

The dihedral angle between the thiophenic ring and the phenyl one is varied from 0° (coplanar rings)

and 90° (perpendicular).

Table S1. hfccs of QBT half molecule, end-capped with a methyl group, varying the dihedral angle

between the thiophenic and phenyl rings

Proton aiso /G

0° 15° 30° 45° 60° 75° 90°

ph2 1.87 1.92 1.98 2.06 2.18 2.34 2.43

ph1 1.81 1.86 1.93 2.04 2.19 2.35 2.43

th2 0.83 0.83 0.74 0.61 0.49 0.44 0.45

th1 -3.94 -3.89 -3.37 -2.62 -1.75 -0.87 -0.41

ph1

ph2

th1 th2

S5

IV - DFT calculations of vibrational properties

Figure S3. Normal modes assigned to features 1 and 2 in the IR spectra of QBT and QDTT (from

DFT calculations on displaced geometries, see Figure 4 and the main text for details on the geometry

displacement procedure). The reported wavenumbers have not been scaled by the 0.98 factor. Red

arrows represent displacement vectors; CC bonds are represented as green (blue) lines of different

thickness according to their relative stretching (shrinking).

Figure S4. Representation of the ECC normal modes of QBT in the optimized and displaced

geometries (see Figure 5a and the main text for details on the geometry displacement procedure).

S6

The reported wavenumbers have not been scaled by the 0.98 factor. Red arrows represent

displacement vectors; CC bonds are represented as green (blue) lines of different thickness according

to their relative stretching (shrinking).

Figure S5. Representation of the ECC normal modes of QDTT in the optimized and displaced

geometries (see Figure 5b and the main text for details on the geometry displacement procedure).

The reported wavenumbers have not been scaled by the 0.98 factor. Red arrows represent

displacement vectors; CC bonds are represented as green (blue) lines of different thickness according

to their relative stretching (shrinking).

S7

V - X-ray data collection

Single crystal data collection of QBT was done at 100 K using synchrotron radiation (𝜆 = 0.77489 Å)

at the BL-13-Xaloc Beamline at Alba-CELLS Synchrotron, Barcelona) under the Proposal Number

2013100590.

Single crystal data collection of QDTT was done at 100 K using a Bruker X8 Prospector APEX-II/CCD

diffractometer equipped with a microfocusing mirror (Cu-Kα radiation, 𝜆 = 1.54178 Å).

The structures were determined using direct methods and refined (based on F2 using all

independent data) by full-matrix least-square methods (SHELXTL 97). All non-hydrogen atoms were

located from different Fourier maps and refined with isotropic displacement parameters.

Further detailed crystallographic information is provided in Table S2.

Table S2. Crystallographic data for QBT and QDTT.

Compound QBT QDTT

Empirical formula

Formula weight

Crystal temperature (K)

Crystal system

Space group

Z

a (Å)

b (Å)

c (Å)

a (deg)

(deg)

(deg)

V (Å3)

Dc (Mg.cm-3)

(mm-1)

F (000)

Rint

Rf/ wRf

All data Rf/ wRf

C19 H23Cl3 O1S1

405.78

100(2)

Monoclinic

P21/n

4

5.8890(12)

18.621(4)

18.648(4)

90.00

92.70(3)

90.00

2042.65(7)

1.320

0.554

848

0.0928

0.0478/ 0.1384

0.0499/ 0.1420

C18H21O1S1.50

301.44

100(2)

Tetragonal

P42212

8

23.474(2)

23.474(2)

6.1972(8)

90.00

90.00

90.00

3414.7(7)

1.173

2.200

1288

0.0310

0.0639/0.1750

0.0758/0.1805

S8

Structural description of QBT.

Dark green crystals of size 0.07 x 0.06 x 0.04 mm were obtained by slow evaporation from a

chloroform-d solution. The asymmetric unit of the crystal contains one QBT and one chloroform-d

molecule.

The packing arrangement shows no π-π interactions. Stabilizing Cmethyl-H···Cl and C-H···O contacts

(2.9 Å and 2.03 Å, respectively) are formed between the solvent molecule and the QBT.

Figure S6. Crystal packing of QBT viewed along the crystallographic a-axis.

S9

Figure S7. Pictures showing the contacts between QBT and chloroform molecules viewed along the

crystallographic a-axis.

Table S3. Bond lengths and angles QBT.

Bond distance (Å)

1 C11 O2 1.244(3)

2 C4 C5 1.402(3)

3 C5 S1 1.748(2)

4 S1 C6 1.743(2)

5 C6 C6 1.391(3)

6 C8 C7 1.366(3)

7 C11 C8 1.484(3)

8 C11 C3 1.475(3)

9 C3 C100 1.362(3)

10 C100 C4 1.435(3)

11 C5 C17 1.419(3)

12 C17 C16 1.376(3)

13 C16 C6 1.417(3)

14 C9 C8 1.524(3)

S10

Table S4. Torsion Angles in QBT.

Torsion angles (˚)

1 C7 C4 C5 C17 -177.3(2)

2 C100 C4 C5 S1 175.8(1)

Table S5. Angles in QBT.

Angles (˚)

1 C5 C4 C7 121.2(2)

2 C17 C5 C4 128.7(2)

Structural description of QDTT.

Dark green crystals were obtained by slow evaporation from a toluene-d8 solution. The asymmetric

unit of QDTT contains only half of the molecule, while the other half is generated through an

inversion center. The packing arrangement of the molecules in the crystal show no π-π interactions

involving any portion of the long conjugated aromatic system. Large empty cavities (135 Å3) are

present in the crystal (Figure S8). This is also confirmed by the low crystal density compared to QBT.

Lattice stability is largely or almost uniquely provided by van der Waals contacts that are formed

between the t-butyl moieties.

Figure S8. Crystal packing of QDTT viewed along the crystallographic c-axis.

S11

Table S6. Bond lengths of QDTT.

Bond distance (Å)

1 O1 C8 1.24(1)

2 C8 C9 1.49(1)

3 C9 C10 1.35(1)

4 C10 C5 1.42(1)

5 C5 C6 1.45(1)

6 C6 C7 1.35(1)

7 C5 C4 1.39(1)

8 C4 S1 1.77(1)

9 S1 C1 1.733(9)

10 C1 C1 1.35(1)

11 C1 C2 1.41(1)

12 C2 C3 1.36(1)

13 C3 C4 1.43(1)

14 C2 S2 1.76(?)

Table S7. Torsion Angles QDTT.

Torsion angle (˚)

1 C10 C5 C4 C3 179.7(9)

2 C6 C5 C4 S1 -172.4(7)

Table S8. Angles QDTT.

Angles (˚)

1 C6 C5 C4 120.1(8)

2 C3 C4 C5 129.6(9)

3 C10 C5 C4 121.3(9)

S12

VI - 1H-NMR spectra of QBT

The spectrum at room temperature (298 K) is consistent with a thermal activation of the rotational

motion about the thiophene-thiophene bond leading to an interconversion between the cis and trans

isomers: according to standard models for exchange processes, the protons of the two conformers are

expected to become equivalent, and their chemical shift to be the averaged value of those at low

temperature. This is also our experimental finding. The presence of narrow linewidths indicates that

the fast motion régime has been reached, that is 𝜏𝛿𝜔 ≪ 1, for the motion; in the expression 𝛿𝜔 is the

difference in frequency of the two merging signals and 𝜏 is the correlation time of the motion.

With increasing of the temperature we observe a broadening of the lines assigned to phenyl protons.

This evidence is consistent with the rotation of the phenyl rings.

8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3

**

**

*

*

*

298 K 600 MHz

Chemical shift (ppm)

313 K 600 MHz

*

Figure S9. 1H-NMR (600 MHz) spectra of sample QBT in deuterated acetone at different

temperatures in the aromatic region. The blue asterisks refer to proton th1 and th2 and the red

asterisks to protons ph1 and ph2.

S13

VII - EPR spectra of QBT in chloroform

The spectrum at room temperature of QBT is shown in Figure S10. The total concentration of QBT is

rather high (1 mM) and the line-width of the observed biradical state is larger than that shown for the

toluene solution in Figure 2 of the main text.

The spectrum has been simulated as sum of two species (see figure S10, red trace) as the best fit

simulation (see Figure S10, grey trace) gave a clear poor reproduction of the spectrum.

Table S9. Hyperfine coupling constant (a) for the proton interaction for QBT in chloroform solution

at room temperature as determined from the simulation of the EPR spectrum in Figure S10 (red

trace) and the relative attribution (see main text).

a (G) Multiplicity Attribution

Species 1

3.78

1.30

0.41

1

2

1

Hth1

Hph

Hth2

Species 2

3.82

1.34

2.12

1

2

1

Hth1

Hph

Hth2

3390 3395

Magnetic field (G)

Figure S10. Cw-EPR spectrum of a 1 mM solution of QBT in deuterated chloroform. In red the

simulation obtained as a 1:1 sum of two species that are interpreted as the two cis/trans conformers.

The simulation parameters are reported in Table S9. In grey the simulation by using a single species.

S14

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