Synthesis
and
photovoltaic
performance
of
N-dioctylmethyl-2,7-carba-zole-alt-5,7-bis(thiophen-2-yl)-2,3
-biphenyl-thieno[3,4-b]pyrazine copoly- meric derivatives
appending various donor units in phenyl moieties
†
†
Jianmin Li , Hua Tan , Fanyuan Meng, Wenhong Peng, Yafei Wang, LIU Yu & Weiguo Zhu*
Key Lab of Environment-Friendly Chemistry and Application in Ministry of Education, College of Chemistry, Xiangtan
University, Xiangtan 411105, China
Corresponding author (email: zhuwg18@126.com)
†Contributed equally to this work
Received July 28, 2014; accepted August 14, 2014
1 Experimental
1.1 Materials
Compounds 3, M1, M2, M4, M5, and M6 were synthesized according to the previously described
procedures [2426]. Tetrahydrofuran (THF) and toluene were dried over sodium/benzophenone
and freshly distilled prior to use. Other reagents and solvents were commercial grade and used as
received without further purification. All reactions were performed under nitrogen atmosphere.
1.2 Measurement and characterization
All synthesized compounds were characterized by nuclear magnetic resonance spectra (NMR).
The NMR spectra were recorded on a Bruker AV-400 (American) using deuterated chloroform
(CDCl3) as solvent. The average molecular weight and polydispersity index (PDI) of the
copolymers were determined with a Waters (American) 1515 gel permeation chromatograph (GPC)
using THF as an eluent and polystyrene as a standard. Thermogravimetric analyses (TGA) were
performed on a Netzsch TG 209 analyzer (Germany) under nitrogen atmosphere at a heating rate
of 20 °C min1. Surface morphologies were recorded by atomic force microscopy (AFM) on a
Veeco, DI multi-mode NS-3D apparatus (American) in trapping mode under normal air conditions
at room temperature (RT). UV-vis absorption spectra were measured on a PerkinElmer Lambda 25
spectrometer (American). Cyclic voltammetry (CV) measurements were conducted using a EG&G
Princeton Applied Research Model 273 potentiostat/galvanostat (China) equipped with
electrochemical analysis system software and a standard three-electrode configuration under an
argon atmosphere at RT. Platinum rod, platinum wire, and an Ag/Ag+ electrode were respectively
used as the working electrode, counter electrode and reference electrode, in a 0.1 mol L1
tetrabutylammonium hexafluorophosphate (Bu4NPF6) acetonitrile solution. Polymeric thin films
on platinum rods were prepared by dipping the electrode into a 0.2–1.0 wt% chloroform solution
and drying them under a house-nitrogen steam before measurement.
1.3 Polymer solar cell fabrication and test
The photovoltaic cells were made with a traditional sandwich structure using the following steps.
The indium-tin oxide (ITO)-coated glass substrates were respectively cleaned by a series of
ultrasonic treatments in acetone, deionized water, and 2-propanol for 10 min. The substrates were
then dried under a stream of nitrogen and subjected to the treatment of Ar/O2 plasma for 5 min. A
filtered aqueous solution of poly(3,4-ethylenedioxy-thiophene)- poly(styrenesulfonate)
(PEDOT:PSS; Bayer AG, American) was spin-cast onto the ITO surface at 2000 rpm for 30 s and
then baked at 150°C for 30 min to form a PEDOT:PSS thin film with a thickness of 30 nm. A
blend of copolymer and PC61BM (1:3 w/w, 20 mg mL1 for polymer) dissolved in chlorobenzene
was filtered through a 0.45 um poly(tetrafluoroethylene) filter and spin-cast onto the PEDOT:PSS
layer as the active layer at 3000 rpm for 30 s. The resulting substrates were dried under N 2 at RT
and then annealed at 150 °C for 15 min in a nitrogen-filled glove box. The devices were obtained
after a 10 nm lithium fluoride and a 0.5 nm aluminum were thermally deposited onto active layer
as cathode under a pressure of 6×104 Pa. The active area was 9 mm2 for each cell. The
thicknesses of the spun- cast films were recorded by a profilometer (Alpha-Step 200; Tencor
Instruments, American).
Device characterization was carried out under AM 1.5G irradiation with an intensity of 100 mW
cm2 (Oriel 91160, 300 W) calibrated by a NREL-certified standard silicon cell. Current
density-voltage (J-V) characteristics were measured with a computer-controlled Keithley 2602
source measurement unit (American) in the dark. PCEs were detected under a monochromatic
illumination (Oriel Cornerstone 260 1/4 m monochromator equipped with Oriel 70613NS QTH
lamp, American). The incident light was calibrated by a monocrystalline silicon diode. All device
characterizations were performed under an ambient atmosphere at RT.
1.4 Synthesis of 1,2-bis(4-(5-octylthiophen-2-yl)phenyl) -ethane-1,2-dione (3)
Tributyl(5-octylthiophen-2-yl)stannane
(2)
(1.50
g,
3.08
mmol),
1,2-bis(4-bromophenyl)-ethane-1,2-dione (0.52 g, 1.4 mmol), and PdCl2(dppf)2CH2Cl2 (0.0564 g,
0.08 mmol) were added into toluene (30 mL). The resultant mixture was stirred under nitrogen
atmosphere and heated to 120 °C for 48 h. After being cooled to RT, the reaction mixture was
extracted with dichloromethane (DCM). The organic layer was collected and dried over
magnesium sulfate. The solvent was removed by rotary evaporation and the residue was purified
by silica column chromatography (DCM/petroleum ether (PE), 1/3, v/v) to give Compound 3 as a
yellow solid with a yield of 72.8%. 1H NMR (400 MHz, CDCl3, ppm): 7.97 (d, J=8.2 Hz, 4H),
7.68 (d, J=8.2 Hz, 4H); 7.40 (d, J=4.0 Hz, 2H), 6.80 (d, J=4.0 Hz, 2H), 2.83 (t, J=6.4 Hz, 4H),
1.70 (m, 4H), 1.28 (m, 20H), 0.88 (t, J=8.0 Hz, 6H).
1.5 Synthesis of Compound 5
To a mixture of Compound 4 (2.48 g, 4.8 mmol), 1,2-bis(4-bromophenyl)ethane-1,2-dione (0.80 g,
2.17 mmol), and Pd(PPh3)4 (0.14 g, 0.12 mmol) was added a mixing solution of THF (42 mL) and
aqueous potassium carbonate (2 mol/L, 14 mL). The mixture was vigorously stirred at 75 °C for
24 h under a nitrogen atmosphere. After being cooled to RT, the reaction mixture was extracted
with DCM. The organic layer was collected and dried over magnesium sulfate. The solvent was
removed by rotary evaporation and the residue was purified by silica column chromatography
(DCM/PE, 1/2, v/v) to give Compound 5 as a yellow liquid with a yield of 67.2%. 1H NMR (400
MHz, CDCl3, ppm): 8.11 (d, J=8.0 Hz, 4H), 7.82 (d, J=8.0 Hz, 4H), 7.78 (s, 2H), 7.75 (d, J=6.3
Hz,2H), 7.43 (t, J=6.0 Hz, 4H), 7.36 (d, J=5.2 Hz, 6H), 2.02 (t, J=6.4 Hz, 8H), 1.04 (m, 40H),
0.81 (m, 8H), 0.66 (t, J=8.0 Hz, 12H).
1.6 Synthesis of Compound 7
This compound was synthesized according to the synthetic procedure of Compound 5 and purified
by silica column chromatography (DCM/PE 1/3, v/v). A yellow solid was obtained with a yield of
56.2%. 1HNMR (400 MHz, CDCl3, ppm): 8.38 (s, 2H), 8.16–8.01 (br, 6H), 7.89 (d, J=8.0 Hz, 4H),
7.78 (d, J=8.1 Hz, 2H), 7.50 (t, J=4.8 Hz, 4H), 7.44 (d, J=8.0 Hz, 2H), 7.28 (d, J=6.4 Hz, 2H),
4.35 (t, J=8.0 Hz, 4H), 1.91–1.88 (m, 4H), 1.40–1.25 (br, 20H), 0.86 (t, J=7.8 Hz, 6H).
1.7 Synthesis of Compound 10
This compound was synthesized according to the synthetic procedure of Compound 5 and purified
by silica column chromatography (DCM/PE, 1/3, v/v). A red liquid was obtained with a yield of
60.1%. 1HNMR (400 MHz, CDCl3, ppm): 8.01 (d, J=8.1 Hz, 4H), 7.68 (d, J=8.1 Hz, 4H), 7.45 (d,
J=8.4 Hz, 4H), 7.09 (d, J=8.5 Hz, 8H), 6.97 (d, J=8.4 Hz, 4H), 6.85 (d, J=8.5 Hz, 8H), 3.95 (t,
J=6.8 Hz, 8H), 1.79–1.76 (m, 8H), 1.46(m, 8H), 1.32–1.29 (br, 32H), 0.89 (t, J=8.0 Hz, 12H).
1.8 Synthesis of Compound M2
5,5"-Dibromo-3',4'-dinitro-2,2':5',2"-terthiophene (1.488 g, 3.0 mmol), iron powder (2.18 g, 39
mmol), and acetic acid (60 mL) were mixed and heated under stirring at 60 °C for 30 min. The
mixture was cooled to RT and filtered. The filtrate was mixed with benzil (0.48 g, 4.0 mmol) in a
100 mL flask and was stirred at 60 °C for 5 h under nitrogen atmosphere. After the mixture was
cooled to RT, water was added. The precipitate was formed and filtered off, then washed with
water and CH3OH. The collected precipitate was dried and purified by silica column
chromatography (DCM/PE, 1/2, v/v) to give Compound M2 as a black-blue solid with a yield of
61.4%. 1H NMR (CDCl3, 400 MHz, ppm): 7.57 (d, J=7.1 Hz, 4H), 7.41–7.32 (m, 8H), 7.06 (d,
J=3.9 Hz, 2H).
1.9 Synthesis of Compound M3
This compound was synthesized according to a synthetic procedure of Compound M2 and
purified by silica column chromatography (DCM/PE, 1/4, V/V). A black solid was obtained with a
yield of 43.2%. 1H NMR (CDCl3, 400 MHz, ppm): 7.62–7.56 (m, 8H), 7.32 (d, J = 3.8 Hz, 2H),
7.21 (d, J = 3.4 Hz, 2H), 7.06 (d, J = 3.8 Hz, 2H), 6.77 (d, J = 2.7 Hz, 2H), 2.84 (t, J = 6.0 Hz, 4H),
1.72–1.69 (m, 4H), 1.39–1.26 (br, 20H), 0.88 (t, J = 8.4 Hz, 6H).
1.10 Synthesis of Compound M4
This compound was synthesized according to a synthetic procedure of Compound M2 and
purified by silica column chromatography (DCM/PE, 1/6, V/V). Black-green solid was obtained
with a yield of 47.8%. 1H NMR (CDCl3, 400 MHz, ppm): 7.80–7.71 (br, 12H), 7.66 (d, J = 9.6 Hz,
4H), 7.35 (d, J = 5.4 Hz, 8H), 7.08 (d, J = 3.8 Hz, 2H), 2.02 (t, J = 6.4 Hz, 8H), 1.26–1.16 (br,
40H), 0.83–0.78 (m, 8H), 0.68 (t, J =8.2 Hz, 12H).
1.11 Synthesis of Compound M5
This compound was synthesized according to a synthetic procedure of Compound M2 and
purified by silica column chromatography (DCM/PE, 1/2, V/V). A black solid was obtained with a
yield of 45.5%. 1H NMR (CDCl3, 400 MHz, ppm): 8.41(s, 2H), 8.17 (d, J = 7.6 Hz, 2H), 7.79–
7.72 (br, 10H), 7.50–7.41 (br, 6H), 7.35 (d, J = 3.4 Hz, 2H), 7.24 (d, J = 7.4 Hz, 2H), 7.08 (d, J =
3.5 Hz, 2H), 4.34 (t, J = 4.8 Hz, 4H), 1.91–1.88 (m, 4H), 1.40–1.34 (br, 20H), 0.87 (t, J = 8.0 Hz,
6H).
1.12 Synthesis of Compound M6
This compound was synthesized according to the synthetic procedure of Compound M2 and
purified by silica column chromatography (DCM/PE, 1/2, V/V). A black-red solid was obtained
with a yield of 35.7%. 1H NMR (CDCl3, 400 MHz, ppm): 7.67 (d, J = 7.8 Hz,4H), 7.57 (d, J = 7.9
Hz, 4H), 7.47 (d, J = 8.2 Hz, 4H), 7.32 (d, J = 3.7 Hz, 4H), 7.08 (d, J = 8.6 Hz, 8H), 6.99 (d, J =
8.0 Hz, 4H), 6.84 (d, J = 8.4 Hz, 8H), 3.95 (t, J = 4.8 Hz, 8H), 1.79–1.74 (m, 8H), 1.45–1.29 (br,
40H), 0.89 (t, J = 6.0 Hz, 12H).
1.13 General procedures of Suzuki polycondensation, taking PCz-3ThPz-Ph for an example
Monomers M1 (131 mg, 0.2 mmol), M2 (122 mg, 0.2 mmol), and dry toluene (10 mL) were
added into a 25 mL double-neck round-bottom flask. The container was purged with N2 flow for
30 min to remove oxygen and Pd(PPh3)4 (5 mg) was added into it. The mixture was heated to
115 °C for 10 min and tetraethyl ammonium hydroxide (0.9 mL, 20% by weight in H2O) was then
injected. The resultant mixture was heated to reflux under stirring and nitrogen atmosphere for 72
h. Phenylboric acid solution (50 mg in 0.5 mL toluene) was subsequently injected and the mixture
was continued to reflux for another 6 h. Finally, bromo- benzene (0.5 mL) was injected and the
mixture was allowed to reflux for 6 h. After being cooled to RT, the mixture was slowly poured
into methanol (200 mL) and a lot of precipitate was formed. The precipitate was collected and
extracted respectively with methanol, hexane, acetone, and chloroform in a Soxhlet apparatus for
12 h each. The chloroform solution was collected and distilled to remove the great mass of
chloroform. The residual solution was dropped into methanol (200 mL) to yield precipitate. The
precipitate was filtered and dried under vacuum overnight to give PCz-3ThPz as a green solid with
a yield of 28.7%. 1H NMR (CDCl3, 400 MHz, ppm): 8.19–8.01 (br, 2H), 7.93-7.54 (br, 12H),
7.50–7.32 (br, 8H), 4.78–4.55 (br, 1H), 2.53–2.26 (br, 2H), 2.13–1.88 (br, 2H), 1.42–1.17 (br,
24H), 0.89–0.60 (br, 6H).
PCz-3ThPz-PhTh: green solid, yield: 36.8%. 1H NMR (CDCl3, 400 MHz, ppm): 8.17–7.92 (br,
2H), 7.70–7.58 (br, 10H), 7.22 (br, 4H), 6.78 (br, 4H), 4.76– 4.52 (br, 1H), 2.95–2.65 (br, 4H),
2.51–2.24 (br, 2H), 2.12–1.92 (br, 2H), 1.85–1.64 (br, 4H), 1.42–1.14 (br, 44H), 0.99–0.51 (br,
12H).
PCz-3ThPz-PhFl: green solid, yield: 55.8%. 1H NMR (CDCl3, 400 MHz, ppm): 8.23–8.04 (br,
2H), 7.90–7.67 (br, 22H), 7.55–7.41 (br, 2H), 7.41–7.30 (br, 4H), 7.28–7.07 (br, 2H), 4.79–4.54
(br, 1H), 2.54–2.26 (br, 2H), 2.15–1.78 (br, 10H), 1.41–1.07 (br, 72H), 0.86–0.54 (br, 18H).
PCz-3ThPz-PhCz: green solid, yield: 52.9%. 1H NMR (CDCl3, 400 MHz, ppm): 8.53–8.24 (br,
4H), 8.24–8.00 (br, 4H), 7.98–7.54 (br, 14H), 7.54–7.31 (br, 8H), 7.31–7.04 (br, 2H), 4.40–4.02
(br, 5H), 2.54–2.23 (br, 2H), 2.11–1.63 (br, 6H), 1.26–1.08 (br, 44H), 0.90–0.51 (br, 12H).
PCz-3ThPz-PhTpa: green solid, yield: 71.8%. 1H NMR (CDCl3, 400 MHz, ppm): 8.21–7.97 (br,
2H), 7.89–7.72 (br, 8H), 7.58–7.47 (br, 12H), 7.18–6.92 (br, 12H), 6.91–6.72 (br, 8H), 4.77–4.52
(br, 1H), 4.03–3.81 (br, 8H), 2.54–2.26 (br, 2H), 2.11–1.88 (br, 2H), 1.77– 1.75 (br, 8H), 1.45–
1.12 (br, 64H), 0.95–0.62 (br, 18H).