Supporting Information
Incorporation of Furan in Low Band Gap Polymers for Efficient Solar
Cells
Claire H. Woo,1,3 Pierre M. Beaujuge,1,2  Thomas W. Holcombe2, Olivia P. Lee2,
and Jean M. J. Fréchet*1,2,3
1Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Departments of 2Chemistry and 3Chemical Engineering, University of California, Berkeley, CA 94720-1460 To whom correspondence should be addressed. Email: frechet@berkeley.edu
Methods and Materials:All reagents from commercial sources were used without further purification, unless otherwise noted. Flash chromatography was performed using Silicycle SiliaFlash ® P60 (particle size 40-63 µm, 230 – 400 mesh) silica gel. Dimethylformamide (DMF) and Tetrahydrofuran (THF) were purchased from Fisher Scientific, and each was purified by passing it under N2 pressure through two packed columns of neutral alumina.  All compounds were characterized by 1H NMR (400 MHz) and 13C NMR (100 MHz) on a Bruker AVB-400 or AVQ-400 instrument.  All NMR spectra were acquired at room t
emperature unless otherwise noted. Data from high-resolution mass spectrometry (HRMS) using electron impact (EI) were obtained by the UC Berkeley mass spectrometry facility.  Matrix assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) was performed on a PerSeptive Biosystems Voyager-DE using 2,2':5',2''-terthiophene as the matrix. Samples were prepared by diluting the monomers in chloroform with the matrix. For polymer molecular weight determination, polymer samples were dissolved in HPLC grade chloroform at a concentration of
1 mg/ml, briefly heated and then allowed to return to room temperature prior to filtering through a 0.
2 µm PVDF filter. SEC was performed using HPLC grade chloroform at a flow rate of 1.0 mL/min on two 300 x 8 mm linear S SDV, 5 µm columns (Polymer Standards Services, USA Inc.) at 30 ºC using a Waters (Milford, MA) separation module and a Waters 486 Tunable Absorption Detector monitored at 254 nm. The instrument was calibrated vs. polystyrene standards (580 – 96,000 Da) and data was analyzed using Millenium 3.2 software.
Synthetic Procedures:
3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (2):A 500 mL three-neck round-bottom flask connected to a condenser and dry nitrogen flow was charged with a stir bar and tert-amyl alcohol (250 mL).  Sodium metal pieces (2.47 g, 107 mmol) were progressively added to the warmed solution of tert-amyl alcohol (60-70 °C). After complete addition of the sodium, the temperature was progressively raised to 120 °C. The mixture was stirred overnight at 120 °C. Furan-2-carbonitrile (1) (10.0 g, 107 mmol) was subsequently added to the hot mixture of sodium alkoxide. Dimethyl succinate (5.23 g, 35.8 mmol) was then added dropwise over a period of 20 min (the reaction mixture turned dark orange-red), and the resulting mixture was stirred for 1.5 h. The reaction mixture was then cooled to room temperature, and the precipitated sodium salt 2 was filtered over a Buchner funnel for collection and dried under vacuum (14.7 g, 87% yield). Compound 2 was used without further purification.
2,5-bis(2-ethylhexyl)-3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (3):Compound2
(3.36 g, 10.8 mmol) and 100 mL of dry DMF were added to a 250 mL two-neck round–bottom flask, equipped with a condenser and stir-bar and placed under N2 atmosphere. The mixture was heated to 120 °C, stirred for 30 min, and 2-ethylhexylbromide (6.05 g, 31.3 mmol) was then added quickly (while at 120 °C).The reaction mixture was subsequently stirred at 140 °C for ca.6 h, and cooled to room temperature. The organic phase was extracted with diethyl ether and washed with water. The diethyl ether was evaporated, and the resulting tacky solid (red) was purified by column chromatography using CHCl3 as eluent. 1.30 g of 3 were isolated (25% yield).1H NMR (400 MHz, CDCl3): δ (ppm) = 8.33 (d, J = 3.6 Hz, 2 H), 7.61 (d, J = 1.3 Hz, 2 H), 6.69 (dd, J = 1.7 Hz, 3.6 Hz, 2 H), 4.04 (d, J = 7.8 Hz, 4 H), 1.80 – 1.68 (m, 2 H), 1.39 – 1.26 (m, 16 H), 0.95 – 0.85 (m, 12 H). 13C (100 MHz, CDCl3): δ (ppm) = 161.4, 145.0, 144.8, 134.1, 120.4, 113.6, 106.6, 46.3, 40.1, 30.7, 28.8, 24.0, 23.2, 14.2, 10.9.  MALDI-TOF MS (m/z): calc’d for C30H40N2O4 [M+] = 492.3; found 492.9.
3,6-bis(5-bromofuran-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (4): Compound3 (1.01 g, 2.05 mmol) was charged in a 100 mL single-neck round–bottom flask filled with 50 mL of CHCl3. The mixture was cooled to 0 °C and stirred while N-bromosuccinimide (NBS) was added in small portions. The mixture was allowed to warm to room temperature and stirred for 2 h following com
plete addition of NBS. The organic phase was extracted with CHCl3and washed with water. The CHCl3was evaporated, and the resulting tacky solid (dark red) was purified by column chromatography using CHCl3as eluent. 0.95 g of 4were isolated (71% yield).1H NMR (400 MHz, CDCl3): δ (ppm) = 8.30 (d, J = 3.7 Hz, 2 H), 6.62 (d, J = 3.7 Hz, 2 H), 3.99 (add, J = 2.7 Hz, 7.4 Hz, 4 H), 1.78 – 1.68 (m, 2 H), 1.39 – 1.24 (m, 16 H), 0.92 (t, J = 7.5 Hz, 6 H), 0.88 (t, J = 7.0 Hz, 6 H). 13C (100 MHz, CDCl3): δ (ppm) = 161.1, 146.4, 132.9, 126.4, 122.4, 115.7, 106.4, 46.4, 40.2, 30.7, 28.9, 23.9, 23.3, 14.2, 10.8. MALDI-TOF MS (m/z): calc’d for C30H38Br2N2O4 [M+] = 648.1; found 648.3.
PDPP2FT (6):4 (200 mg, 0.307 mmol), 2,5-bis(trimethylstannyl)-thiophene (5) (126 mg, 0.307 mmol),
Pd2(dba)3 (2 mol %) and P(o-tol)3 (8 mol %) were charged with a 50 mL Schlenk tube, cycled with N2 and subsequently dissolved in 6 mL of degassed chlorobenzene. The mixture was stirred for 24 h at 110 °C. The reaction mixture was allowed to cool to 55 °C, 15 mL of CHCl3 was added, and the strongly complexing ligand N,N-diethylphenylazothioformamide (CAS# 39484-81-6) was subsequently added (as a palladium scavenger). The resulting mixture was stirred for 1 h at 55°C, and precipitated into methanol (200 mL). The precipitate was filtered through a Soxhlet thimble and purified via Soxhlet extraction for 12 h with methanol and 1 h with hexanes, followed by collection in chloroform. The chloroform solution was then passed through a plug of silica, neutral alumina, and celite (1:1:1), concentrated by evaporation and precipitated into methanol (200 mL). The polymer 6 was filtered off as a dark solid (162 mg). SEC analysis: M n = 66 kDa, PDI = 2.05 (See Figure S1a).
2,5-bis(trimethylstannyl)furan (8):Compound 7(2.0 g, 8.85 mmol) and 30 mL of dry THF were added to a 100 mL two-neck round–bottom flask with stir bar, and placed under N2 atmosphere. The mixture was cooled to -78 °C, and n-BuLi (2.5 M in hexanes) (18.2 mmol, 7.4 mL) was added dropwise over 30 min (while at -78 °C).Following complete addition of n-BuLi, the reaction mixture was stirred for an additional 15 min at -78 °C. It was subsequently allowed to reach room temperature and stirred for 1 h. The reaction mixture was cooled down to -78 °C, Me3SnCl (18.6 mmol, 3.70 g) was charged all at once, and the mixture was stirred at -78 °C for 15 min. It was then allowed to reach room temperature and stirred for 12 h. The organic phase was extracted with diethyl ether and washed with water. Diethyl ether was evaporated, and the resulting oil (yellow) was passed through a plug of basic alumina using hexanes as eluent. Hexanes were evaporated, and the resulting oil (colorless) was distilled under reduced pressure (68-72 °C at 180 mTorr) and 0.74 g of 8 were isolated (21% yield). 1H NMR (400 MHz, CDCl3): δ (ppm) = 6.71 (s, 2 H), 0.40 (m,18 H). 13C (100 MHz, CDCl3): δ (ppm) = 165.2, 120.3, -9.0.
PDPP3F (9): The same polymerization and purification protocols as those described for PDPP2FT (6) were followed. Polymer 9 was collected as a dark and brittle solid (58 mg). SEC analysis: M n = 29 kDa, PDI = 2.02 (See Figure S1b).
>reaction mass

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