X. Liu et al. / Polymer 55 (2014) 1707e1715
1709
white solid. 1H NMR (300 MHz, CDCl3)
0.34e0.30 (s, 18H). 13C NMR (75 MHz, CDCl3)
155.58, 152.54, 152.31, 130.64, 130.41, 130.27, 130.21, 130.07, 129.85,
129.21, 129.12, 129.04, ꢀ0.75, ꢀ1.10, ꢀ1.46.
d
(ppm): 7.10e7.09 (m, 2H),
(ppm): 155.81,
temperature was raised to room temperature and kept stirring for
6 h. The reaction mixture was poured into water and extracted with
ethyl acetate three times. The ethyl acetate phase was washed with
brine, dried with anhydrous MgSO4, and then the solvent was
removed under vacuum. The crude product was purified by column
chromatography (silica gel, petroleum ether/dichloromethane, 3:1,
as eluent) twice to yield 1.65 g (50%) of the product as colorless oil.
d
2.2.2. 1,4-Dibromo-2,3-difluorobenzene (2)
In a 150 mL two-neck round-bottom flask, (2,3-difluoro-1,4-
phenylene)bis(trimethylsilane) 1 (10.34 g, 40 mmol) was added
slowly into bromine (6.3 mL, 120 mmol) at 0 ꢂC. The mixture was
heated to 58 ꢂC and stirred for 2 h. Then bromine (1 mL, 20 mmol)
was added again and stirred for 1 h at 58 ꢂC. The mixture was
cooled down to 0 ꢂC and added saturated NaHCO3. Ethyl acetate
was added to extract the organic part. The ethyl acetate phase was
washed with brine, dried with anhydrous MgSO4, and then the
solvent was removed under vacuum. The crude product was puri-
fied by reduced pressure distillation to yield 8.7 g (84%) of the
1H NMR (300 MHz, DMSO)
2.05 (m, 2H), 1.83e1.74 (m, 2H), 1.38e0.83 (m, 16H), 0.81e0.66 (m,
14H). 13C NMR (75 MHz, CDCl3)
(ppm): 150.74, 150.52, 148.14,
d
(ppm): 5.02 (tt, J ¼ 4.8 Hz, 1H), 2.13e
d
147.92, 136.13, 136.10, 136.08, 95.66, 95.56, 95.52, 95.42, 64.89,
39.02, 32.61, 31.95, 29.04, 25.94, 23.17, 14.15, 10.97.
2.2.7. 4,7-Bis(4-(2-ethylhexyl)thiophen-2-yl)-2-(1-(20-ethylhexyl)-
3-ethylhexyl)-5,6-difluoro-2,1,3-benzotriazole (7)
In a 100 mL two-neck round-bottom flask, 4,7-dibromo-2-(1-
product as colorless oil. 1H NMR (300 MHz, CDCl3)
d
(ppm): 7.25e
(20-ethylhexyl)-3-ethylhexyl)-5,6-difluoro-2,1,3-benzotriazole
6
7.13 (m, 2H). 13C NMR (75 MHz, CDCl3)
d
(ppm): 150.31, 150.08,
(2.755 g, 5 mmol) and tributyl(4-(2-ethylhexyl)thiophen-2-yl)
stannane (6.068 g, 12.5 mmol) were dissolved in anhydrous toluene
(30 mL). The solution was purged with argon for 30 min and
dichlorobis(triphenylphosphine)palladium(II) (50 mg) was added
at room temperature under argon protection. The mixture was
heated up to 110 ꢂC for 3 days. The solvent was evaporated under a
vacuum, and the crude product was purified by column chroma-
tography (silica gel, petroleum ether/dichloromethane, 10:1, as
eluent) to yield 1.69 g (78%) of the product as a colorless oil. 1H NMR
146.94, 146.71, 128.34, 128.31, 128.29, 109.57, 109.47, 109.44, 109.34.
2.2.3. 1,4-Dibromo-2,3-difluoro-5,6-dinitrobenzene (3)
In a 500 mL round-bottom flask, 45 mL of concentrated sulfuric
acid was added and cooled to 0 ꢂC in an ice water bath. Fuming
nitric acid (50 mL) and 1,4-dibromo-2,3-difluorobenzene 2 (8.1 g,
30 mmol) were added slowly and stirred for 24 h at 70 ꢂC. The
mixture was then precipitated into ice water. The resulting yellow
solid was filtered and purified by column chromatography (silica
gel, petroleum ether/dichloromethane, 1:4, as eluent) to yield 3.8 g
(35%) of the product as a yellow solid. 13C NMR (75 MHz, CDCl3)
(300 MHz, CDCl3)
d (ppm): 7.97 (s, 2H), 7.11 (s, 2H), 5.08 (m, 1H),
2.67e2.58 (dd, J ¼ 6.6 Hz, 4H), 2.26e2.22 (m, 2H), 1.80e1.68 (m,
4H), 1.45e1.13 (m, 28H), 0.98e0.81(m, 16H), 0.78e1.72 (m,
J ¼ 6.9 Hz, 6H).
d
(ppm): 150.78, 150.56, 147.28, 147.05, 140.38, 105.02, 104.85,
104.71, 104.67, 104.53, 104.37.
2.2.8. 4,7-Bis(5-bromo-4-(2-ethylhexyl)thiophen-2-yl)-2-(1-(20-
ethylhexyl)-3-ethylhexyl)-5,6-difluoro-2,1,3-benzotriazole (8)
To a stirred solution of 4,7-bis(4-(2-ethylhexyl)thiophen-2-yl)-
2-(1-(20-ethylhexyl)-3-ethylhexyl)-5,6-difluoro-2,1,3-
2.2.4. 3,6-Dibromo-4,5-difluorobenzene-1,2-diamine (4)
In a 250 mL two-neck round-bottom flask, 1,4-dibromo-2,3-
difluoro-5,6-dinitrobenzene 3 (3.3 g, 9.2 mmol), iron powder
(7.3 g, 130 mmol) and acetic acid (130 mL) were stirred at 45 ꢂC for
6 h under argon protection. The solution was cooled down to room
temperature and poured into cold 5% NaOH solution (400 mL).
Then ethyl acetate was added to extract the organic part three
times. The ethyl acetate phase was washed with NaHCO3 solution,
dried with anhydrous MgSO4, and then the solvent was removed
under vacuum to yield 2.5 g (89%) of the product as light yellow
benzotriazole 7 (2.737 g, 3.5 mmol) in anhydrous THF (25 mL) was
added N-bromosuccinimide (NBS) (1.28 g, 7.18 mmol) in darkness.
The mixture was stirred at room temperature for 24 h, and a
saturated solution of sodium bicarbonate was added. The product
was extracted with methylene chloride, dried (MgSO4), filtered, and
then silica gel was added. The slurry was concentrated in vacuo,
and the resulting solid purified by column chromatography (silica
gel, petroleum ether/dichloromethane, 12:1, as eluent). After
repeating the chromatography step a second time, a fluorescent
yellow solid (93%) was obtained in purity sufficient for polymeri-
powder. 1H NMR (300 MHz, DMSO)
(75 MHz, DMSO) (ppm): 141.07, 140.83, 137.97, 130.06, 130.04,
94.65, 94.50, 94.36.
d
(ppm): 5.16 (s, 4H). 13C NMR
d
zation. 1H NMR (300 MHz, CDCl3)
d (ppm): 7.98 (s, 2H), 5.19 (d,
2.2.5. 4,7-Dibromo-5,6-difluoro-1H-benzotriazole (5)
In 150 mL round-bottom flask, 3,6-dibromo-4,5-
J ¼ 6.7 Hz, 1H), 2.65e2.52 (m, 2H), 2.40e2.12 (m, 2H), 1.89e1.47 (m,
a
16H), 1.28e1.18 (m, 23H), 1.03e0.65 (m, 18H). 13C NMR (75 MHz,
difluorobenzene-1,2-diamine 4 (2.4 g, 8 mmol) was dissolved in
100 mL of AcOH at room temperature. A solution of NaNO2 (2.76 g,
40 mmol) in 20 mL of H2O was added in 20 min. The mixture was
stirred at room temperature for 1 h and precipitated into ice water.
The resulting brown solid was filtered and recrystallized from
CDCl3) d (ppm): 148.84, 148.58, 145.49, 145.23, 141.53, 136.89,
131.80, 131.46, 113.59, 109.62, 64.73, 40.01, 35.67, 35.43, 33.65,
32.75, 32.58, 28.60, 28.46, 25.67, 25.38, 23.04, 22.86, 14.13, 14.08,
13.97, 10.86.
benzene to yield 2.3 g (84%) of the product as a light gray solid. 13
C
2.3. Polymerization
NMR (75 MHz, DMSO)
135.16, 94.67.
d (ppm): 149.47, 149.21, 146.17, 145.93,
Both of the polymerizations were carried out by Stille coupling
reactions with an equivalently molar ratio of the distannyl mono-
mers to the dibromo monomer 8 under argon protection [36,37].
The purifications of the polymers were conducted in air. A typical
procedure for the copolymerization and the characterizations for
the two copolymers are given below.
2.2.6. 4,7-Dibromo-2-(1-(20-ethylhexyl)-3-ethylhexyl)-5,6-
difluoro-2,1,3-benzotriazole (6)
In a 100 mL round-bottom flask, 4,7-dibromo-5,6-difluoro-1H-
benzotriazole 5 (1.9 g, 6 mmol), 1-(20-ethylhexyl)-3-ethylheptanol
(3.1 g, 12 mmol) and PPh3 (3.15 g, 12 mmol) was dissolved in
50 mL of anhydrous THF. Diisopropyl azodicarboxylate (DIAD)
(2.43 g, 12 mmol) was added in 20 min at 0 ꢂC under argon pro-
tection. After the solution was stirred for 10 min at 0 ꢂC, the
2.3.1. PFBTA-3T
Carefully purified 4,7-bis(5-bromo-4-(2-ethylhexyl)thiophen-
2-yl)-2-(1-(20-ethylhexyl)-3-ethylhexyl)-5,6-difluoro-2,1,3-