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ARTICLE
TABLE 1 Molecular Weights and Thermal Properties of
3.91–3.95 (m, 4H), 1.82–1.84 (m, 2H), 1.21–1.38 (m, 16H),
0.76–1.20 (m, 12H). 13C NMR (75 MHz, CDCl3): d 161.7,
140.4, 135.2, 130.5, 129.8, 128.4, 107.9, 45.8, 39.1, 30.2,
28.3, 23.5, 23.0, 14.0, 10.5.
PCTDPP
Mn
Mw
PDI
Tg (ꢀC)
Td (ꢀC)a
PCTDPP
18,000
38,160
2.12
150
385
3,6-Bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)
pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (M1)
a
Temperature at which 5 wt % loss of the initial weight occurred.
NBS (0.36 g, 2.0 mmol) was added to a solution of 2 (0.50 g,
0.95 mmol) in CHCl3 (30 mL) in a two-neck round-bottom
flask covered with Al foil. After stirring at room temperature
for 48 h, the reaction mixture was poured into water (100
mL) and extracted with CHCl3 (3 ꢂ 100 mL). The organic
layer was dried (MgSO4) and the solvent was evaporated
under reduced pressure. The crude product was purified
chromatographically (SiO2) to yield Compound M1 (0.34 g,
53%).
After dissolving the components, the resultant solution was
spin-coated onto ITO/PEDOT:PSS substrates at 1500 rpm for
60 s. The films were then left to dry at room temperature.
No additional thermal treatment was applied to the active
layers. The films were subjected to cathode deposition
through a shadow mask to result in a device area of 0.12
cm2. Aluminum was used as the cathode. The devices were
characterized for their photoresponse using an Agilent 4156
semiconductor parameter analyzer, under AM 1.5 radiation
(100 mW/cm2). The spectral mismatch factor was calculated
by comparison of the solar simulator spectrum and the AM
1.5 spectrum at room temperature.
1H NMR (300 MHz, CDCl3): d 8.62 (d, J ¼ 4.5 Hz, 2H), 7.19
(d, J ¼ 4.5 Hz, 2H), 3.91–3.95 (m, 4H), 1.79–1.80 (m, 2H),
1.20–1.37 (m, 16H), 0.82–0.88 (m, 12H). 13C NMR (75 MHz,
CDCl3): d 161.4, 139.4, 135.4, 131.4, 131.1, 119.0, 108.0,
46.0, 39.1, 30.1, 28.3, 23.5, 23.0, 14.0, 10.4. Anal. Calcd. for
C
30H38Br2N2O2S2: C, 52.79; H, 5.61; N, 4.10. Found: C, 52.50;
Synthetic Procedures
4H-Cyclopenta[2,1-b:3,4-b0]dithiophene (3) was synthesized
according to literature procedures.48–51 The synthetic proce-
dures for the preparation of the monomers M1 and M2 and
the copolymer PCTDDP are described in Schemes 1 and 2.
H, 5.34; N, 3.77%.
4,4-Dioctylcyclopenta[2,1-b:3,4-b0]dithiophene (4)
KOH (3.14 g, 56.2 mmol) was added slowly to a mixture of 3
(2.00 g, 11.2 mmol), 1-bromooctane (8.67 g, 44.9 mmol),
and KI (80 mg, 0.48 mmol) in DMSO (55 mL) at 0 ꢀC. After
stirring at room temperature overnight, the mixture was
poured into water and extracted with hexane (3 ꢂ 100 mL).
The organic layer was dried (MgSO4) and the solvent evapo-
rated under reduced pressure. The crude product was puri-
fied chromatographically (SiO2) to yield 4 (3.61 g, 80%).
3,6-Di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (1)
A mixture of Na (0.490 g, 21.3 mmol) and a catalytic
amount of FeCl3 was dissolved in tert-amyl alcohol (10 mL)
by heating at 90 ꢀC for 2 h. After cooling to 50 ꢀC, thio-
phene-2-carbonitrile (0.990 mL, 10.6 mmol) was added and
then the mixture was again heated at 90 ꢀC. A solution of
dibutyl succinate (1.00 mL, 4.26 mmol) in tert-amyl alcohol
(5 mL) was added dropwise over 2 h and then the mixture
was maintained at 90 ꢀC for 20 h. After cooling to 50 ꢀC,
glacial AcOH was added and then the mixture was heated
under reflux for 10 min before being filtered. The residue
was washed several times with hot MeOH and water, and
then the solid was dried under vacuum to yield 1 (0.8 g,
63%). This compound was used directly in the next step
without purification.
1H NMR (300 MHz, CDCl3): d 7.12 (d, J ¼ 4.8 Hz, 2H), 6.91
(d, J ¼ 4.8 Hz, 2H), 1.77–1.86 (m, 4H), 1.12–1.55 (m, 20H),
0.80–0.94 (m, 10H). 13C NMR (75 MHz, CDCl3): d 158.1,
136.4, 124.4, 121.6, 53.2, 37.7, 31.8, 30.0, 29.3, 29.2, 24.5,
22.6, 14.1.
2,5-Bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]
pyrrole-1,4(2H,5H)-dione (2)
A solution of 2-ethylhexyl bromide (4.89 mL, 27.5 mmol) in
DMF (30 mL) was added dropwise to a mixture of Com-
pound 1 (2.50 g, 8.33 mmol), K2CO3 (3.83 g, 27.8 mmol),
and 18-crown-6 (0.25 g, 0.95 mmol) in DMF (50 mL) at 120
ꢀ
ꢀC and then the mixture was maintained at 120 C overnight.
After cooling to room temperature and filtering, the product
was dissolved in CHCl3 washed with water (3 ꢂ 100 mL),
and then dried (MgSO4). The solvent was evaporated under
reduced pressure and the crude product was purified
through chromatography (SiO2) to yield 2 (2.05 g, 47%).
1H NMR (300 MHz, CDCl3): d 8.86 (dd, J ¼ 1.2, 3.9 Hz, 2H),
7.60 (dd, J ¼ 1.2, 4.8 Hz, 2H), 7.24 (dd, J ¼ 1.2, 4.8 Hz, 2H),
FIGURE 1 Normalized UV-vis absorption spectra of PCTDPP.
SYNTHESIS AND CHARACTERIZATION OF A NARROW-BANDGAP POLYMER, CHEN ET AL.
1671