Synthesis and Photovoltaic Properties of Two-Dimensional Conjugated Polymers with Tunable

Supplementary Information

Synthesis and Photovoltaic Properties of Two-Dimensional Conjugated Polymers with Tunable Pendant Acceptor Groups

Lingyan Liao1,2, Wei Zhang2, Zuo Xiao2, Jiamin Cao2, Zhanpeng Liu1, Qiqun Zuo3, and Liming Ding2

1College of Chemistry and Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, XiangtanUniversity, Xiangtan 411105, China

2NationalCenter for Nanoscience and Technology, Beijing100190, China

3Jiahong Optoelectronics, Suzhou215151, China

Correspondence: Dr L Ding, NationalCenter for Nanoscience and Technology, Beijing 100190, China. E-mail: ; Dr Z Liu, College of Chemistry and Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, XiangtanUniversity, Xiangtan 411105, China. E-mail: .

Content

1. General characterization

2. Solar cell fabrication and characterization

3. Synthesis of monomers and copolymers

4. Molecular weights and thermal properties of P1-P4

5. TGA plots of P1-P4

6. Cyclic voltammograms of P1-P4

7. J-Vcurves for solar cells based on P1-P4

8. NMR spectra

1. General characterization

1H NMR and 13C NMR spectra were measured on a Bruker Avance-400 spectrometer. Thermogravimetry analysis was performed on a Perkin-Elmer Diamond TG/DTA Instrument. Absorption spectra were measured on a SHIMADZU UV-1800 spectrophotometer. Molecular weights of polymers were measured on a Waters 1515 series GPC coupled with UV-vis detector using tetrahydrofuran as eluent and polystyrenes as standards. ElementalanalysiswascarriedoutusingaFLASHEA1112elementalanalyzer.Cyclic voltammetry was conductedon a Shanghai Chenhua CHI620 electrochemical workstation in a 0.1 mol/L tetrabutylammonium hexaﬂuorophosphate (Bu4NPF6) acetonitrile solution with a glassy-carbon electrode coated with polymer film as the working electrode, a Pt wire as the counter electrode, and a Ag/Ag+ electrode as the reference electrode. All potentials were corrected against Fc/Fc+.

2. Solar cell fabrication and characterization

Solar cells were fabricated on indium tin oxide (ITO)-coated glass substrates, which were cleaned by ultrasonication with detergent, deionized water, acetone, and isopropanol for 20 min respectively. PEDOT:PSS (Clevios™ P Al 4083) was spin-coated onto ITO glass and then baked at 140 °C for 10 min in air. Polymer:PC61BM blend dissolved in ODCB was spin-coated onto PEDOT:PSS layer. The film was then annealed at 110 °C for 10 min in glovebox. After annealing, Ca (10 nm) and Al (100 nm) were successively deposited by thermal evaporation under high vacuum (<10-6 mbar). The effective area for the cells is 7.57 mm2. J-V curves were measured under AM 1.5G illumination from a calibrated solar simulator (Newport) (86 mW/cm2).

3. Synthesis of monomers and copolymers

Materials.Tetrahydrofuran (THF) and toluene were dried over Na/benzophenone and freshly distilled prior to use. Other chemicals used in this work were commercial products and used as received. M5 was synthesized according to the literature.1-2

1-(5-Bromothiophen-2-yl)-2-ethylhexan-1-one(1). 2-Bromothiophene (4.0 g, 24.5 mmol),2-ethylhexanoylchloride(4.0g, 24.5 mmol) and dichloromethane (100 mL) were put into a 250 mL flask, which was kept in an ice-salt bath. Aluminium chloride (3.43 g, 25.7 mmol) was added in small portions within 1 h.The resulting dark greenmixture was stirred at room temperature and monitored by TLC. The reaction was stopped until 2-bromothiophene disappeared completely. The reaction mixture was poured into a mixture of ice and concentrated hydrochloride acid, and then extracted by dichloromethane twice. Theorganic layer was washed with saturated sodium chloridesolutionfor three times and dried over Na2SO4.The solvent was removed by rotary evaporation.Column chromatography (petroleum ether/dichloromethane: 1/1) afforded pure compound 1(2.0 g, 28%) as a colourless liquid. 1HNMR(400 MHz, CDCl3), δ:7.47 (d, 1H, J = 4.0 Hz, thiophene), 7.12 (d, 1H, J = 4.0 Hz, thiophene), 3.00-3.07 (m, 1H, CH), 1.22-1.81 (m, 8H, CH2), 0.85-0.91 (m, 6H, CH3).13CNMR(100 MHz, CDCl3), δ: 196.45, 147.05, 131.54, 131.28, 122.60, 49.53, 32.18, 29.84, 25.91, 22.84, 13.89, 12.05.

2-Ethyl-1-(5-(thiophen-3-yl)thiophen-2-yl)hexan-1-one (2). To a stirredsolution of compound 1 (1.85 g, 6.4 mmol) and thiophene-3-boronic acid(1.26 g, 9.8 mmol) in anhydrous THF (100 mL) were added K2CO3 (5.96 g, 43.2 mmol) and Pd(PPh3)4 (0.69 g, 0.597 mmol) at room temperature under Ar. The mixture was reﬂuxed for 24 h. After removal of the solvent, the residual was poured intowater and extracted with dichloromethanefor three times. The organic layerswere combined and dried over Na2SO4. After removal of solvent,column chromatography (petroleum ether/dichloromethane: 1/2) afforded pure compound 2 (1.7 g, 91%)as a colourless liquid. 1HNMR(400 MHz, CDCl3), δ:7.66 (d, 1H, J = 4.0 Hz, thiophene), 7.54-7.55 (m, 1H, thiophene), 7.38-7.40 (m, 1H, thiophene), 7.34-7.36 (m, 1H, thiophene), 7.22 (d, 1H, J = 4.0 Hz, thiophene), 3.08-3.15 (m, 1H, CH), 1.22-1.83 (m, 8H, CH2), 0.81-0.92 (m, 6H, CH3).13CNMR(100 MHz, CDCl3), δ: 197.33, 147.14, 143.38, 134.91, 132.37, 126.93, 125.96, 123.98, 121.91, 49.69, 32.33, 29.89, 26.04, 22.88, 13.92, 12.12.

1-(5-(2,5-Dibromothiophen-3-yl)thiophen-2-yl)-2-ethylhexan-1-one (M1).To a stirredsolution of compound 2 (1.7 g, 5.8 mmol) in DMF (25mL)was added NBS (2.07 g, 11.6 mmol) in one portion under Ar. After stirring at room temperature for 48 h, the reaction solution was poured into ice water. The mixture was extracted by chloroform and washed with saturated sodium chloridesolutionfor three times. The organic layerwas dried over Na2SO4. Column chromatography (petroleum ether/dichloromethane: 1/2) afforded pure M1(0.3 g, 11%) as a pale yellow oil.1HNMR(400 MHz, CDCl3), δ:7.68 (d, 1H, J = 4.0 Hz, thiophene), 7.42 (d, 1H, J = 4.0 Hz, thiophene), 7.16 (s, 1H, thiophene), 3.09-3.16 (m, 1H, CH), 1.20-1.82 (m, 8H, CH2), 0.85-0.92 (m, 6H, CH3).13CNMR(100 MHz, CDCl3), δ:197.60, 144.78, 143.22, 134.42, 131.62, 130.67, 127.31, 112.39, 109.28, 50.00, 32.37, 30.02, 26.10, 23.03, 14.09, 12.26.

2,5-Dibromothiophene-3-carbaldehyde (3). Compound 3 (white solid) was synthesized by following similar procedures for M1. Reactants: thiophene-3-carbaldehyde (1.38 g, 12.3 mmol) and NBS (4.37 g, 24.6 mmol). Yield: 1.5 g, 45%. 1HNMR(400 MHz, CDCl3), δ:9.77 (s, 1H, CHO), 7.32 (s,1H, thiophene).3

(E)-3-(2,5-Dibromothiophen-3-yl)-2-(thiophen-2-yl)acrylonitrile (4). To a stirred solution of compound 3 (1.0 g, 3.7 mmol) in ethanol (25 mL)were added2-thiopheneacetonitrile (0.46 g,3.7 mmol) and potassium tert-butoxide (0.21 g, 1.8 mmol). The mixture was stirred for 4 h under N2, filtered and washed twice with ethanol, to give a pale yellow solid (1.2 g, 86%).1HNMR(400 MHz, CDCl3), δ:7.93(s, 1H, CH=C), 7.40 (d, 1H, J = 3.6 Hz, thiophene), 7.35 (d, 1H, J = 4.8 Hz, thiophene), 7.28 (s, 1H, thiophene), 7.08 (t, 1H, J = 4.4 Hz, thiophene).13CNMR(100 MHz, CDCl3), δ:138.53, 135.18, 129.41, 128.33, 127.90, 127.86, 126.99, 117.92, 116.26, 113.07, 106.89.

(E)-3-(2,5-Dibromothiophen-3-yl)-2-(5-(2-ethylhexanoyl)thiophen-2-yl)acrylonitrile (M2).M2 (pale yellow solid) was synthesized by following similar procedures for compound 1. Reactants:compound 4 (0.5 g, 1.33 mmol) and 2-ethylhexanoylchloride(0.45 g, 2.76 mmol). Yield: 0.45 g, 67%.1HNMR(400 MHz, CDCl3), δ:7.95 (s, 1H, CH=C), 7.64 (d, 1H, J = 4.0 Hz, thiophene), 7.44 (s, 1H, thiophene), 7.40 (d, 1H, J = 4.0 Hz, thiophene), 3.08-3.15 (m, 1H, CH), 1.23-1.81 (m, 8H, CH2), 0.85-0.92 (m, 6H, CH3).13CNMR(100 MHz, CDCl3), δ: 197.23, 145.86, 134.80, 132.58, 131.01, 129.11, 128.55, 127.42, 126.79, 115.56, 113.54, 106.17, 50.32, 32.19, 29.83, 25.91, 22.86, 14.57, 12.72.

4-(Thiophen-3-yl)benzaldehyde (5). Compound 5 (white solid) was synthesized by following similar procedures for compound 2. Reactants: 4-bromobenzaldehyde (4.7 g, 25.4 mmol) and thiophene-3-boronic acid(5.0 g, 39.2 mmol). Yield: 4.0 g, 83%.1HNMR(400 MHz, CDCl3), δ:10.02 (s, 1H, CHO), 7.91 (d, 2H, J = 8.0 Hz,benzene), 7.75(d, 2H, J = 8.0 Hz, benzene), 7.61 (t, 1H, J = 4.4 Hz,thiophene), 7.44 (t, 2H, thiophene).13CNMR(100 MHz, CDCl3), δ:191.64, 141.49, 140.91, 135.01, 130.40, 126.91, 126.77, 126.13, 122.51.

4-(2,5-Dibromothiophen-3-yl)benzaldehyde (6). Compound 6 (white solid) was synthesized by following similar procedures for M1. Reactants: compound 5 (2.2 g, 11.7 mmol) and NBS (4.16 g, 23.4 mmol). Yield: 2.0 g, 50%.1HNMR(400 MHz, CDCl3), δ:10.05 (s, 1H, CHO), 7.94 (d, 2H, J = 8.4 Hz, benzene), 7.68(d, 2H, J = 8.0 Hz, benzene), 7.06 (s, 1H, thiophene).13CNMR(100 MHz, CDCl3), δ:191.57, 140.73, 139.88, 135.65, 131.32, 129.85, 129.13, 112.04, 109.16.

(E)-3-(4-(2,5-Dibromothiophen-3-yl)phenyl)-2-(thiophen-2-yl)acrylonitrile (7).Compound 7 (pale yellow solid) was synthesized by followingsimilar procedures for compound 4. Reactants: compound 6 (0.85 g, 2.46 mmol) and 2-thiopheneacetonitrile (0.39 g, 3.18 mmol). Yield: 1.0 g, 90%.1HNMR(400 MHz, CDCl3), δ:7.92 (d, 2H, J = 8.0 Hz, benzene), 7.60 (d, 2H, J = 8.0 Hz,benzene), 7.41 (d, 1H, J = 3.2 Hz, thiophene), 7.39 (s, 1H, CH=C), 7.33 (d, 1H, J = 4.8 Hz, thiophene), 7.09-7.10 (t, 1H,J = 4.4 Hz,thiophene), 7.06 (s, 1H, thiophene).13CNMR(100 MHz, CDCl3), δ:140.91, 139.14, 138.59, 135.91, 132.97, 131.36, 129.23, 128.98, 128.19, 127.50, 126.46, 116.77, 111.75, 108.53, 106.51.

(E)-3-(4-(2,5-Dibromothiophen-3-yl)phenyl)-2-(5-(2-ethylhexanoyl)thiophen-2-yl)acrylonitrile (M3). M3 (yellow solid) was synthesized by following similar procedures for compound 1. Reactants:compound 7 (0.53 g, 1.17 mmol) and 2-ethylhexanoylchloride (0.4 g, 2.46 mmol). Yield: 0.35 g, 52%.1HNMR(400 MHz, CDCl3), δ:7.95 (d, 2H, J = 8.0 Hz, benzene), 7.67 (d, 1H, J = 4.0 Hz, thiophene),7.64 (d,2H, J = 8.0 Hz, benzene), 7.54 (s, 1H, CH=C), 7.42 (d, 1H, J = 4.0 Hz, thiophene), 7.06 (s, 1H, thiophene), 3.10-3.16 (m, 1H, CH),1.25-1.83 (m, 8H, CH2), 0.83-0.92 (m, 6H, CH3).13CNMR(100 MHz, CDCl3), δ:197.32, 146.38, 145.48, 142.15, 140.75, 136.80, 132.89, 132.22, 131.21, 130.49, 130.00, 128.98, 128.33, 127.11, 116.30, 111.99, 108.92, 105.93, 50.39, 32.29, 29.93, 26.01, 22.93, 14.64, 11.57.

2-Fluoro-4-(thiophen-3-yl)benzaldehyde (8). Compound 8 (white solid) was synthesized by following similar procedures for compound 2. Reactants: 4-bromo-2-fluorobenzaldehyde (3.1 g, 15.27 mmol) and thiophene-3-boronic acid (3.0 g, 23.62 mmol). Yield: 2.7 g, 86%.1HNMR(400 MHz, CDCl3), δ:10.34 (s, 1H, CHO), 7.89 (t, 1H, J = 8.0 Hz,benzene), 7.62 (m, 1H, benzene), 7.50 (d, 1H, J = 8.0 Hz, benzene), 7.46-7.36 (m, 3H, thiophene).13CNMR(100 MHz, CDCl3), δ:186.61, 166.38, 163.81, 143.78, 139.88, 129.29, 127.24, 125.92, 123.30, 122.48, 113.68.

4-(2,5-Dibromothiophen-3-yl)-2-fluorobenzaldehyde (9).Compound 9 (white solid) was synthesized by following similar procedures for M1. Reactants:Compound 8 (2.0 g, 9.7 mmol) and NBS (3.45 g, 19.4 mmol). Yield: 2.54 g, 72%.1HNMR(400 MHz, CDCl3), δ:10.38 (s, 1H, CHO), 7.93 (t, 1H, J = 7.6 Hz,benzene), 7.35-7.42 (m, 2H, benzene), 7.04 (s, 1H, thiophene).13CNMR(100 MHz, CDCl3), δ:186.54, 165.70, 163.12, 141.93, 139.51, 131.03, 128.89, 124.80, 116.55, 112.42, 109.80.

(E)-3-(4-(2,5-Dibromothiophen-3-yl)-2-fluorophenyl)-2-(thiophen-2-yl)acrylonitrile (10).Compound 10 (pale yellow solid) was synthesized by following similar procedures for compound 4. Reactants: compound 9 (1.8 g, 4.94 mmol) and 2-thiopheneacetonitrile (0.61 g, 4.94 mmol). Yield: 2.0 g, 86%.1HNMR(400 MHz, CDCl3), δ:8.30 (t, 1H,J = 8.0 Hz, benzene), 7.61 (s, 1H, CH=C), 7.43-7.45(m, 1H, benzene), 7.39-7.42 (m, 1H, benzene),7.32-7.37 (m, 2H, thiophene), 7.09-7.11 (m, 1H,thiophene), 7.05 (s, 1H, thiophene).13CNMR(100 MHz, CDCl3), δ:161.91, 159.39, 139.88, 139.08, 137.88, 131.25, 130.09, 128.34, 128.06, 127.19, 124.81, 121.33, 116.62, 115.89, 112.24, 109.26, 108.34.

(E)-3-(4-(2,5-Dibromothiophen-3-yl)-2-fluorophenyl)-2-(5-(2-ethylhexanoyl)thiophen-2-yl)acrylonitrile (M4).M4 (yellow solid) was synthesized by following similar procedures for compound 1. Reactants:compound 10 (0.3 g, 0.64 mmol) and 2-ethylhexanoylchloride (0.22 g, 1.34 mmol). Yield: 0.16 g, 42%.1HNMR(400 MHz, CDCl3), δ:8.34 (t, 1H, J = 8.0 Hz, benzene), 7.79 (s, 1H, CH=C), 7.67 (d, 1H, J = 4.0 Hz, thiophene), 7.42-7.45 (m, 2H, benzene), 7.35-7.38 (m, 1H, thiophene), 7.05 (s, 1H, thiophene), 3.09-3.16 (m, 1H, CH), 1.22-1.84 (m, 8H, CH2), 0.85-0.93 (m, 6H, CH3).13CNMR(100 MHz, CDCl3), δ:197.20, 145.83, 139.54, 138.68, 161.99, 159.56, 132.72, 131.92, 131.04, 130.18, 129.13, 127.45, 125.64, 124.01, 115.82, 112.28, 109.47, 107.50, 49.17, 32.20, 29.86, 25.92, 22.86, 14.56, 11.48.

Synthesis of P1. In a 100 mL flask, M1 (0.16 g, 0.35 mmol)and M5 (0.27 g, 0.35 mmol) were dissolved in toluene (40 mL) and flushed with Ar for 10 min. Then, Pd(PPh3)4(0.022 g, 0.019 mmol) was added.Arflush was kept for another 20 min. The solution was heated to refluxand stirred for 48 h under Ar. The reaction solution was cooled to room temperature and added dropwise into methanol (100 mL).The precipitate was collected and further purified by Soxhlet extractionwith methanol, hexane, and chloroform in sequence. The chloroform fraction was concentrated and precipitated from methanol and filtered. The red solid was dried under vacuumfor 10 h to obtain P1.Yield:0.14 g, 52%.1HNMR(400 MHz, CDCl3), δ:7.63 (br, 1H, thiophene), 7.56-7.58 (br, 2H, thiophene), 7.44(br, 1H, thiophene), 7.23 (br, 1H, thiophene), 4.15-4.25 (br, 4H, OCH2), 3.12 (br, 1H, COCH), 1.28-1.83 (br, 26H, CH2, CH), 0.87-1.11 (br, 18H, CH3).Anal. Calcd for (C42H54O3S4)n: C 68.62 H 7.40;found C 68.17 H 7.30.

Synthesis of P2. P2 (dark gray solid) was synthesized by following the same procedures for P1 using M2 (0.19 g, 0.38 mmol) and M5 (0.30 g, 0.38 mmol) as starting materials. Yield: 0.26 g,84%.1HNMR(400 MHz, CDCl3), δ:7.26-7.84 (br, 6H, CH=C, thiophene), 4.19 (br, 4H, OCH2), 3.16 (br, 1H, COCH), 1.25-1.79 (br, 26H, CH2, CH), 0.90-0.91 (br, 18H, CH3). Anal. Calcd for (C45H55NO3S4)n: C 68.75 H 7.05 N 1.78;found C 68.24 H6.97 N 1.74.

Synthesis of P3.P3 (dark red solid) was synthesized by following the same procedures for P1 using M3 (0.11 g, 0.19 mmol) and M5 (0.14 g, 0.19 mmol) as starting materials. Yield:0.12 g,71%.1HNMR(400 MHz, CDCl3), δ:7.95 (br,1H, CH=C), 7.26-7.67 (br,9H, benzene, thiophene), 3.99-4.24 (br, 4H, OCH2), 3.14 (br, 1H, COCH), 1.26-1.79 (br, 26H, CH2, CH), 0.88-1.07 (br, 18H, CH3). Anal. Calcd for (C51H59NO3S4)n: C 71.04 H 6.90 N 1.62; found C 68.88 H 6.84 N 1.50.

Synthesis of P4.P4 (dark red solid) was synthesized by following the same procedures for P1 using M4 (0.1 g, 0.17 mmol) and M5 (0.13 g, 0.17 mmol) as starting materials. Yield:0.13 g,84%.1HNMR(400 MHz, CDCl3), δ:8.39 (br, 1H, CH=C), 7.01-7.83 (br, 8H, benzene, thiophene), 4.16-4.18 (br, 4H, OCH2), 3.17 (br, 1H, COCH), 1.32-1.81 (br, 26H, CH2, CH), 0.91-1.09 (br, 18H, CH3). Anal. Calcd for (C51H58FNO3S4)n: C 69.59 H 6.64 N 1.59; found C 69.39H 6.66 N 1.61.

4. Molecular weights and thermal properties of P1-P4

Table S1. Molecular Weights and Thermal Properties of the Polymers

Polymers / Mn (kg/mol) / Mw (kg/mol) / PDI / Td (°C)a
P1 / 20.8 / 49.2 / 2.36 / 325
P2 / 27.8 / 115.3 / 4.15 / 333
P3 / 19.6 / 68.5 / 3.49 / 283
P4 / 17.0 / 43.2 / 2.54 / 325

a Decomposition temperature at 5% weight loss.

5. TGA plots of P1-P4

FigureS1 TGA curves for the polymers at a scan rate of 10 °C /min under N2.

6. Cyclic voltammograms of P1-P4

Figure S2. Cyclic voltammograms of the polymer films measured in CH3CN containing 0.1 M Bu4NPF6.

7. J-V curves for solar cells based on P1-P4

Figure S3. J-V curves for solar cells based on P1-P4 under AM1.5G illumination (86 mW/cm2)

8. NMR spectra

1H NMR of M1 (CDCl3)

1H NMR of M2 (CDCl3)

1H NMR of M3 (CDCl3)

1H NMR of M4 (CDCl3)

1H NMR of P1 (CDCl3)

1H NMR of P2 (CDCl3)

1H NMR of P3 (CDCl3)

1H NMR of P4 (CDCl3)

References

1 Hou, J. H., Park, M. H., Zhang, S. Q., Yao, Y., Chen, L. M., Li, J. H. & Yang, Y. Bandgap and molecular energy level control of conjugated polymer photovoltaic materials based on benzo[1,2-b:4,5-b′]dithiophene. Macromolecules41, 6012-6018 (2008).

2 Zhang, G. B., Fu, Y. Y., Zhang, Q. & Xie, Z. Y. Benzo[1,2-b:4,5-b′]dithiophene-dioxopyrrolothiophen copolymers for high performance solar cells. Chem. Commun.46, 4997-4999 (2010).

3 Gallazzi,M. C., Toscano,F., Paganuzzi,D., Bertarelli,C., Farina,A. Zotti, G.Polythiophenes with unusual electrical and optical properties based on donor acceptor alternance strategy. Macromol. Chem. Phys.202, 2074-2085 (2001).