Thiophene-Bithiazole Based Metal-Free Dye As DSSC Sensitizer: Effect of Co-Adsorbents

SUPPORTING INFORMATION

Thiophene-bithiazole based metal-free dye as DSSC sensitizer: Effect of co-adsorbents on photovoltaic efficiency

JAYANTHY S PANICKERa,b, BIJITHA BALAN*,a,SURAJ SOMAN*,a,TANWISTHA GHOSHa,b and VIJAYAKUMAR C NAIRa,b

aPhotosciences and Photonics Group, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Trivandrum 695 019, India

bAcademy of Scientific and Innovative Research (AcSIR), Trivandrum 695 019, India

e-mail: ;

Table of contents

Synthesis of TP1

Synthesis of 81 and 92 reported in literature.

Figure S1.Synthetic scheme of TP1.

Synthesis of 2-bromo-3-hexyl-5-formylthiophene (8):A vilsmeier reagent was prepared using POCl3 (2.22 mL, 24.27 mmol, 2 eq.) anddimethylformamide (8.45 mL, 109.21 mmol, 9 eq.) and it was added to solution of 2-bromo-3-hexylthiophene (3 g, 12.13 mmol, 1 eq.) in dichloroethane at 0 C under argon. After being stirred for 12 h at 60 C, the mixture was poured into ice water,neutralised with Na2CO3 and then extracted with CH2Cl2 and dried over Na2SO4. It was purified by column chromatography (15% Ethyl acetate-hexane). Pure product was obtained as a light yellow liquid (Yield - 85%). 1H NMR (500 MHz, CDCl3)9.74 (s, 1H), 7.46 (s, 1H), 2.57 (t, 2H), 1.63-1.57 (m, 2H), 1.36-1.30 (m, 6H), 0.90-0.87 (t, 3H);HRMS: m/z = 274 (M+).

Synthesis of 4-hexyl-5-phenylthiophene-2-carbaldehyde (9): 2-bromo-3-hexyl-5-formyl-thiophene (547 mg, 1.99 mmol, 1 eq.), 4,4,5,5-tetramethyl-2-phenyl-1,3,2-dioxaborolane (486 mg, 2.39 mmol, 1.2 eq.) andK2CO3 (2.74 g, 19.87 mmol, 10 eq.) were dissolved in THF - H2O mixture (9:1). Air was removed out of the set up and replaced by nitrogen, three times by using a freeze-thaw-pump method, then Pd(PPh3)4 was added under nitrogen-counter flow. The reaction mixture was heated and stirred under nitrogen for two days, then poured into water and extracted with CH2Cl2.After washing the combined organic layer with brine and water, it was dried over Na2SO4 and the solvent evaporated purified by column chromatography (1:1 CHCl3-hexane). Yield: 89%. 1H NMR (500 MHz, CDCl3) 9.86 (s, 1H), 7.66 (s, 1H), 7.46-7.40 (m, 5H), 2.66 (t, J 7.75, 2H), 1.64-1.60 (m, 2H), 1.32-1.22 (m, 6H), 0.85 (t, J 6.75, 3H).HRMS: m/z = 295.11 (M+ + Na).

Synthesis of (Z)-2-cyano-3-(4-hexyl-5-phenylthiophen-2-yl) acrylic acid (TP1)

To a mixture of 4-hexyl-5-phenylthiophene-2-carbaldehyde (100 mg, 0.367 mmol, 1 eq.) and cyanoacetic acid (62.43 mg, 0.367 mmol, 2 eq.) were added acetonitrile (10 mL) and piperidine (0.04mL, 0.44 mmol, 1.2 eq.) at room temperature. The solution was refluxed overnight. After cooling to room temperature, the organic phase was separated and the aqueous layer extracted with CH2Cl2. The combined organic phases were washed with brine, dried with MgSO4, and concentrated in vacuo. The crude residue was purified by column chromatography (DCM: MeOH = 9: 1) to give adduct as a yellow liquid. Yield: 70%. 1H NMR (500 MHz, CDCl3) 8.30 (s, 1H), 7.70 (s, 1H), 7.46-7.43 (m, 5H), 2.69-2.63 (m, 2H), 1.63-1.57 (m, 2H), 1.29-1.25 (m, 6H), 0.85 (t, J 4.5, 3H).13C NMR (125 MHz, CDCl3) 148.90, 146.61, 139.86, 139.67, 132.72, 132.00, 128.11, 127.87, 127.76, 115.02, 30.44, 29.61, 28.67, 28.00, 27.35, 21.51, 13.00. HRMS: m/z = 362.11 (M+ + Na).

Synthesis of TP2

Synthesis of 103 and 114 reported in theliterature.

Figure S2.Synthetic scheme of TP2.

Synthesis of 3, 3’,-dihexyl-2, 2’-bithiophene-5-carbaldehyde (10) :

2-bromo-3-hexyl-5-formylthiophene (3.45 g, 12.54 mmol, 1 eq.) and 3-hexylthiophene-2-boronic acid pinacolester (4 g, 13.78 mmol, 1.1 eq.) were weighed in a two necked RB flask and dissolved in anaerobic THF- H2O mixture (2:1). K2CO3 (17 g, 125 mmol, 10 eq.) was added to the mixture and the flask was connected to a reflux condenser equipped with a septum. Air was pumped out of the set up and replaced by nitrogen using freeze-thaw-pump method, then Pd(PPh3)4 was added under Ar-counter flow. The reaction mixture was refluxed for two days under nitrogen atmospherethen poured in to water and extracted with CH2Cl2.After washing the combined organic layer with brine and water, it was dried over Na2SO4 and the solvent evaporated under reduced pressure and purified by column chromatography (1:1 CHCl3-hexane).Yield: 85%. 1H NMR (500 MHz, CDCl3) 9.87 (s, 1H),7.66 (s, 1H), 7.36 (d, J 5, 1H), 6.99 (d, J 5, 1H), 2.57-2.52 (m, 4H), 1.60-1.52 (m, 4H), 1.27-1.25 (m, 12H), 0.85 (t, 6H);HRMS: m/z = 362.17 (M+).

Synthesis of 5-bromo-3,3’,-dihexyl-2,2’-bithiophene-5-carbaldehyde (11):

N-bromosuccinnimide (71 mg, 0.4 mmol, 1.1 eq.) was added in small portions to solution of 3,3’-dihexyl-2,2’-bithiophene-5-carbaldehyde (132 mg, 0.36 mmol, 1 eq.) in chloroform and acetic acid (1:1) at 0 °C. After being stirred for 6hr at room temperature, the reaction mixture was poured into water and extracted with dichloromethane. The organic layer was thoroughly washed with water, aqueous Na2CO3, brine and again with water and dried over Na2SO4 and the solvent evaporated and purified by column chromatography (1:1 CHCl3-hexane). Pure product was obtained as a light yellow liquid. Yield: 95%. 1H NMR (500 MHz, CDCl3) 9.87 (s, 1H), 7.64 (s, 1H), 6.97 (s,1H), 2.55 (t,2H), 2.47 (t, 2H), 1.58 - 1.50 (m, 4H), 1.30 - 1.21 (m, 12H), 0.87 (t, 3H), 0 .85 (t, 3H); HRMS: m/z = 442.08 (M+).

Synthesis of 5-phenyl-3, 3’-dihexyl-2,2’-bithiophene-5-carbaldehyde (12):

5-bromo-3,3’-dihexyl-2,2’-bithiophene-5-carbaldehyde (1 g, 2.26 mmol, 1 eq.) and phenyl-2-boronic acid pinacol ester (508 mg, 2.49 mmol, 1.1 eq.) were weighed in a two necked RB flask and dissolved in anaerobic THF - H2O mixture (2:1). K2CO3 (3.08 g, 22.65 mmol, 10 eq.) was added to the mixture and the flask was connected to a reflux condenser equipped with a septum. Air was pumped out of the set up and replaced by Ar, three times by using a freeze-thaw-pump method, then Pd(PPh3)4 (130 mg, 0.11 mmol, 0.05 eq.) was added under Ar-counter flow. The reaction mixture was refluxed for two days, then poured in to water and extracted with CH2Cl2. After washing the combined organic layer with brine and water, it was dried over Na2SO4 and the solvent evaporated and purified by column chromatography (1:1 CHCl3-hexane). 1H NMR (500 MHz, CDCl3) 9.87 (s, 1H), 7.65 (s, 1H), 7.60 (d, J 7.5, 2H), 7.39 (t, J 7.5, 2H), 7.29 (t, J 7.25, 1H), 7.21 (s, 1H), 2.61 (t, J 7.75, 2H), 2.55 (t, J 7.75, 2H), 1.59 - 1.58 (m, 4H), 1.26 (t, J 5.5, 12H), 0.86 (t, J 6.5, 6H). 13C NMR (125 MHz, CDCl3) 182.86, 144.95, 144.22, 143.65, 142.39, 139.89, 137.73, 133.80, 128.96, 127.93, 127.90, 127.85, 126.54, 125.68, 125.03, 31.62, 31.58, 30.70, 30.51, 29.20, 29.10, 28.99, 28.87, 22.58, 22.56, 14.08, 14.06.HRMS: m/z = 461.19(M+ + Na).

Synthesis of TP2:

To a mixture of 5-phenyl -3, 3’,-dihexyl-2, 2’-bithiophene -5-carbaldehyde(180 mg, 0.410 mmol, 1 eq.) and cyanoacetic acid (69.80 mg, 2.50 mmol, 2 eq.) were added acetonitrile (10 mL) and few drops of piperidine added at room temperature. The solution was refluxed overnight. After cooling to room temperature, the organic phase was separated and the aqueous layer extracted with CH2Cl2. The combined organic phases were washed with brine, dried with MgSO4, and concentrated in vacuo. The crude residue was purified by column chromatography (DCM: MeOH = 9: 1) to give adduct as a yellow orange liquid. 1H NMR (500 MHz, CDCl3)8.28 (s, 1H), 7.73 (s, 1H), 7.60 (d, J 8, 2H), 7.39 (t, J 7.5, 2H), 7.31 (t, J 7.25, 1H), 7.21 (s, 1H), 2.62 (t, J 7.75, 2H), 2.57 (t, J 7.75, 2H), 1.59-1.58 (m, 4H), 1.28-1.26 (m, 12H), 0.85 (t, J 4.75, 6H). 13C NMR (125 MHz, CDCl3) 146.18,144.24, 143.45, 142.99, 140.18, 138.34, 133.94, 132.71, 128.23, 127.93, 127.52, 126.90, 125.17, 124.66, 124.09, 115.01, 30.57, 30.50, 29.64, 29.45, 28.67, 28.30, 28.06, 27.99, 27.70, 21.53, 13.05, 13.01.HRMS: m/z = 528.20 (M+ + Na).

Figure S3.1H NMR of 5.

Figure S4.13C NMR of 5.

Figure S5.HRMS of 5.

Figure S6.1H NMR of 6.

Figure S7.13C NMR of 6.

Figure S8.HRMS of 6.

Figure S9.1H NMR of 7.

Figure S10.13C NMR of 7.

Figure S11.HRMS of 7.

Figure S12.1H NMR of BT1.

Figure S13.13C NMR of BT1.

Figure S14.HRMS of BT1.

Figure S15. 1H NMR of 9.

Figure S16.13C NMR of 9.

Figure S17.HRMS of 9.

Figure S18.1H NMR of TP1.

Figure S19.13C NMR of TP1.

Figure S20.1H NMR of 10.

Figure S21.1H NMR of 11.

Figure S22.1H NMR of 12.

Figure S23.13C NMR of 12.

Figure S24.HRMS of 12.

Figure S25.1H NMR of TP2.

Figure S26.13C NMR of TP2.

Figure S27.HRMS of TP2.

Photophysical Properties

Figure S28. Film state absorption of BT1 on TiO2.

Figure S29. Absorption spectra of BT1 with increasing percentage of water.

Figure S30. Emission spectra of BT1 with increasing percentage of water.

Figure S31.(a) Absorption and (b) emission spectra of TP1 and TP2 in THF.

Table S1. Photovoltaic performance parameters of BT1 in the presence of different co-adsorbents

Composition of electrolyte: [a] 0.6 M BMII, 0.1 M LiI, 0.05 M I2, 0.5 M TBP. [b]Commercial electrolyte from dyesol

7. References

[1]ZhangJ,WuG,HeC, Dengab Dand LiY2011J. Mater. Chem.21 3768.

[2]LiW, Maddux Tand YuL1996Macromolecules29 7329.

[3]GuoY,SuJ, AnZ,Chen X and ChenP 2015J.Mol. Struc.1094195.

[4]HayashiN, NishiharaT, MatsukihiraT, NakashimaH, MiyabayashiK,MiyakeMand HiguchiH2007Bull. Chem. Soc. Jpn. 80371.

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