Synthesis and photovoltaic properties of new low bandgap isoindigo-based conjugated polymers

Article abstract of DOI:10.1021/ma102357b

A series of new isoindigo-based low banbap polymers, containing thiophene, thieno[3,2-b]thiophene and benzo[1,2-b:4,5-b′]dithiophene as donors, have been synthesized by Stille cross-coupling reaction. Their photophysical, electrochemical and photovoltaic properties have been investigated. These new polymers exhibit broad and strong absorption between 400 and 800 nm with absorption maxima around 700 nm. The HOMO energy levels of polymers vary between -5.20 and -5.49 eV and the LUMO energy levels range from -3.66 to -3.91 eV. The optical bandgaps of the polymers are optimized for solar cell applications and they are at about 1.5 eV. Polymer solar cells (PSC) based on these new polymers were fabricated with device structures of ITO/PEDOT:PSS/polymers: PC ₇₁BM (1:2, w/w)/LiF/Al. The photovoltaic properties of the polymers have been evaluated under AM 1.5G illumination at 100 mW/cm² with a solar simulator. The combination of broad absorption, optimal bandgap and well matched energy levels with those of PCBMs makes these isoindigo-based low bandbap polymers promising materials for photovoltaic applications.

Full text of DOI:10.1021/ma102357b

ARTICLE
pubs.acs.org/Macromolecules
Synthesis and Photovoltaic Properties of New Low Bandgap
Isoindigo-Based Conjugated Polymers
Guobing Zhang,† Yingying Fu,‡ Zhiyuan Xie,*,‡ and Qing Zhang*,†
†Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University,
Shanghai 200240, China
‡State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Science,
Changchun 130022, China
S Supporting Information
b
ABSTRACT: A series of new isoindigo-based low banbap polymers, containing thiophene,
thieno[3,2-b]thiophene and benzo[1,2-b:4,5-b0]dithiophene as donors, have been synthe-
sized by Stille cross-coupling reaction. Their photophysical, electrochemical and photo-
voltaic properties have been investigated. These new polymers exhibit broad and strong
absorption between 400 and 800 nm with absorption maxima around 700 nm. The
HOMO energy levels of polymers vary between -5.20 and -5.49 eV and the LUMO
energy levels range from -3.66 to -3.91 eV. The optical bandgaps of the polymers are
optimized for solar cell applications and they are at about 1.5 eV. Polymer solar cells
(PSC) based on these new polymers were fabricated with device structures of ITO/
PEDOT:PSS/polymers: PC71BM (1:2, w/w)/LiF/Al. The photovoltaic properties of the
polymers have been evaluated under AM 1.5G illumination at 100 mW/cm2 with a solar simulator. The combination of broad
absorption, optimal bandgap and well matched energy levels with those of PCBMs makes these isoindigo-based low bandbap
polymers promising materials for photovoltaic applications.
’ INTRODUCTION
indigo, isoindigo itself is brown colored and has absorption maxima
at 365 and 490 nm in dimethyl sulfoxide solution. Isoindigo also
shows better stability than indigo when expose to light.5 Crystal-
lographic study on alkyl substituted isoindigo shows that the central
carbon-carbon double bond has an E configuration and is
conjugated with two indole heterocycles to form perfect planar π-
conjugated structure.7 Recently, there are some successful examples
of introduction high performance dyes into conjugated polymers
and oligomers.3c,8 Polymers based on electron deficient diketopyr-
rolopyrrole (DPP) dye as acceptors have achieved power conver-
sion efficiencies (PCEs) of 5.5%.9 Isoindigo, which contains two
lactam rings, is another electron-deficient dye. The perfect planar
π-conjugated structure and a strong electron-withdrawing effect
make it ideal monomer for synthesis of donor/acceptor low
bandgap conjugated polymer for organic solar cell applications.
Isoindigo-based oligothiophenes and polymers have been reported
by Reynolds and co-workers.10 The isoindigo-based oligomers
showed interesting absorption spectra and low HOMO energy
levels.10a Here, we present the synthesis of five new low bandgap
polymers based on isoindigo (ID) units and different electron-
donors (thiophene, thieno[3,2-b]thiophene and benzo[1,2-b:4,5-b0]-
dithiophene), and the characterization of their thermal, optical,
electrochemical, and photovoltaic properties.
Organic photovoltaic (OPV) with many advantages such as
low cost, lightweight, and solution processability may become an
important part of renewable energy in the future.1 Low band gap
conjugated polymers have attracted considerable attention recently
because of their applications in organic solar cell devices. Bulk-
heterojunction (BHJ) based on blending of electron-donating
conjugated polymers and high-electron-affinity fullerene derivatives
such as PCBMs is the most successful device structure for
polymer solar cell so far.2 Many new conjugated polymers
have been synthesized for high performance OPV appli-
cations.3 The design rules for donor polymers in fullerene
based BHJ devices are low HOMO energy level for high open
circuit voltage, low band gap for large solar photon harvest,
balanced crystallinity and solubility for high hole mobility
and for optimal morphology, and well-matched HOMO/
LUMO energy levels between polymers and those of full-
erenes for efficient charge separation.4 Development of new
monomers may lead to synthesis of interesting polymers with
tailor-made photophysical, electrochemical and other prop-
erties to fulfill those requirements for high performance solar
cells.
(E)-1H,10H-[3,30]biindolylidene-2,20-dione (isoindigo) which
can be obtained from various natural sources is one of the indigoid
natural organic dyes.5 Its derivatives are active constituents in some
traditional Chinese medicine and have recently emerged as a
promising scaffold for antileukemia activities.6 Unlike blue-colored
Received: October 15, 2010
Revised:
January 13, 2011
Published: February 04, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Monomers
Scheme 2. Synthesis of Isoindigo-Based Polymers
’ RESULTS AND DISCUSSION
48.9% yield, respectively. The tin monomers 5, 6, and 7 were
prepared according to the literature methods.11 The polymers
were synthesized by Stille cross-coupling reactions with 1:1
monomer ratio in presence of tris(dibenzylideneacetone)-
dipalladium (Pd2(dba)3) as catalyst and triphenylarsine as ligand
to give purple-blue materials. The crude polymer was purified by
precipitating in methanol and washing with methanol and hexane
in a Soxhlet extractor for 24 h each. The residue was extracted
with hot chloroform or chlorobenzene in an extractor for 24 h.
Polymer PT-ID1, PTT-ID1, and PBDT-ID are soluble and can
be extracted with hot chloroform or chlorobenzene. After
removing solvent, purple-blue solids were collected. Polymer
PT-ID2 and PTT-ID2 with 2-ethylhexyl side chains were
Synthesis and Characterization of Polymers. The syn-
thetic routes for monomers and polymers were illustrated in
Scheme 1 and 2. The commercially available 6-bromoisatin and
6-bromooxindole were refluxed in acetic acid and hydrochloric
acid under nitrogen to give a brown solid 6,60-dibromoisoindigo
(1) in 77.6% yield.10 Because of the strong π-π interactions and
hydrogen bonding, the brown solid is only slightly soluble in
common organic solvents. To improve the solubility of isoindigo
monomer, branched 2-octyldodecyl and 2-ethylhexyl side chains
were attached to both lactam nitrogen atoms. The alkylated 6,60-
dibromoisoindigo monomers 2 and 3 was obtained in 64.2% and
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Table 1. Molecular Weights and Thermal Properties of
Polymers
polymer
yield (%)
Mna (kDa)
Mwa (kDa)
PDIa
Td (°C)b
PT-ID1
69.2
72.3
76.6
17.2
37.6
21.9
36.1
127.8
32.6
2.1
3.4
1.5
397
397
348
PTT-ID1
PBDT-ID
a Mn, Mw, and PDI of polymers were determined by GPC using
polystyrene standards with THF as eluent. b The temperature of 5%
weight-loss under nitrogen.
insoluble in any solvent. The large branched side chains or
multiple short branched side chains are required to ensure the
solubility of isoindigo based polymers. The chemical structures
of the polymer PT-ID1, PTT-ID1, and PBDT-ID were verified
1
by H NMR spectroscopy. The spectra were included in Sup-
porting Information. These three polymers showed good solu-
bility in solvents such as chloroform and chlorobenzene. The
number-average molecular weights (Mn) and polydispersity
indexes of the polymers were determined by gel permeation
chromatography (GPC) using polystyrenes as standards with
tetrahydrofuran as eluent. GPC data are listed in Table1. The
reported number-average molecular weights (Mn) were mea-
sured at room temperature. They may not accurately reflect
average molecular weight of single polymer chain when there is
strong intermolecular interaction and polymer aggregation.
Thermal Stability. Thermogravimetric analyses of polymers
were displayed in the Table 1 and Figure S1 in the Supporting
Information. The temperature of 5% weight-loss was chose as
onset point of decomposition (Td). Polymer PT-ID1, PTT-ID2,
and PBDT-ID were thermally stable up to 397, 397, and 348 °C.
Thermal properties of polymers are important for device applica-
tion. The new polymers showed good thermal stability for
application in PSCs and other optoelectronic devices. Neither
polymers displayed noticeable glass transition in differential
scanning calorimetry (DSC) analysis.
Figure 1. Normalized UV-vis spectra of isoindigo-based polymers (a)
in chloroform solution and (b) as thin film.
absorption bands for PT-ID1, PTT-ID1, and PBDT-ID were at
786, 800, and 803 nm, respectively. The optical bandgaps (Eogpt)
were calculated from the absorption edges of solid state films.
The optical bandgaps of PT-ID1, PTT-ID1, and PBDT-ID were
1.58, 1.55, and 1.54 eV, respectively. The absorption spectra of
polymer films showed good overlap with solar flux at sea level,
which has a maximum at about 700 nm.
Optical Properties. The optical properties of polymers were
also analyzed. The UV-vis absorption spectra of the polymers in
chloroform solution and as thin films are shown in Figure 1. The
optical properties of the polymers were summarized in Table 2.
Polymer PT-ID1 showed two absorption bands in chloroform
solution. The first absorption band maximum at 466 nm is
relatively weak compared to isoindigo-based oligothiophenes,10a
Electrochemical Properties. The electrochemical properties
of polymers were investigated by cyclic voltammetry (CV). The
cyclic voltammograms of PT-ID1, PTT-ID1, and PBDT-ID
films are shown in Figure 2. The potentials were referenced to
the ferrocene/ferrocenium redox couple (Fc/Fcþ). The redox
potential of Fc/Fcþ was assumed an absolute energy level of
-4.8 eV to vacuum.12 The redox potential of Fc/Fcþ was measured
under the same condition as polymer sample and was located at
0.09 V related to the Ag/Agþ electrode. The CV data were
summarized in Table 2. The onset oxidation potentials of PT-
ID1, PTT-ID1, and PBDT-ID were located at 0.78, 0.72, and
and the second absorption band of PT-ID1 is broad and red-
abs
max
shifted (λ at 684 nm) compared to isoindigo-based oligomer
(λ
abs
max
at 579 and 560 nm,). The red-shifted absorption of the
polymer PT-ID1 is expected because of increasing effective
conjugation in polymer. However, the relatively weak absorption
of polymer in short wavelength (400-530 nm) compared to
oligomers need further study. The PTT-ID1 polymer with
thieno[3,2-b]thiophene as donor showed similar optical proper-
ties but its absorption spectrum was further red-shift (λmax at
717 nm). Polymer PBDT-ID showed almost the same absorp-
tion spectra as PT-ID1 in the range of 500-800 nm. All the three
polymers exhibited shoulder peaks in the visible region. The film
absorption spectra of polymers were depicted in Figure 1b. The
absorption maxima of PT-ID1, PTT-ID1, and PBDT-ID solid
films were at 694, 718, and 688 nm, respectively. The absorption
spectra of polymer films showed little change compared to their
solution absorption spectra. The branched side chains may have
adverse effect on the intermolecular interaction of polymers and
prevent effective intermolecular stacking. The edges of the film
0.49 eV respectively. The HOMO energy levels of the polymers
ox
onset
were calculated according to the equation: HOMO = -(E
þ
4.71) eV. The HOMO energy levels of polymers are shown in
Table 2. The HOMO energy level of PT-ID1 was the lowest
at -5.49 eV, the HOMO energy level of PTT-ID1 was at
-5.43 eV, and the HOMO energy level of PBDT-ID was the
highest at -5.20 eV among three isoindigo-based polymers. The
relatively lower HOMO energy levels of these isoindigo-based
polymers can be attributed to electron deficient lactam rings in
isoindigo repeating units. The LUMO energy levels of PT-ID1,
PTT-ID1, and PBDT-ID were -3.91, -3.88, and -3.66 eV
calculated from the optical band gaps and HOMO energy levels
of the polymers. These new polymers possess relatively low
HOMO energy level for high open circuit voltage and suitable
LUMO energy level for charge separation, together with low
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Table 2. Optical and Redox Properties of Polymers
solution λ (nm)
film λ (nm)
oxidation (V, vs Ag/Agþ in CH3CN)
Eogpt (eV)a
E
(V)
HOMO (eV)b
E
(V)c
red
onset
LUMO (eV)d
abs
max
abs
max
abs
onset
ox
onset
polymer
λ
λ
λ
PT-ID1
684
717
680
694
718
688
786
800
803
1.58
1.55
1.54
0.78
-5.49
-5.43
-5.20
-0.80
-0.83
-3.91
-3.88
PTT-ID1
PBDT-ID
0.72
0.49
-1.05
ox
onset
-3.66
a Calculated from UV absorption spectrum of polymer film by the equation: band gap =1240/λ . b HOMO = -(4.71 þ E ). c E
= E
- Eogpt
.
abs
onset
red
onset
ox
onset
d LUMO = Eogpt þ HOMO.
Figure 3. Charge-carrier mobilities of polymer/PC71BM (1:2) blend
films.
Figure 2. Cyclic voltammograms of isoindigo-based polymers thin
films.
Photovoltaic Properties. Polymer solar cell devices with
polymer PT-ID1, PTT-ID1, and PBDT-ID as electron donors
and PC71BM as electron acceptor were fabricated. The device
structure was ITO/PEDOT:PSS/polymer:PC71BM/LiF/Al. So-
lar cell devices were characterized under AM 1.5G illumination at
100 mW/cm2 with a solar simulator. The photovoltaic perfor-
mances of the devices with different polymer/PC71BM weight
ratio were summarized in Table 3. The polymer/PC71BM weight
ratio of 1:2 showed the best device performance. Figure 4
displayed the current-voltage curves of the devices and corre-
sponding values of open-circuit voltage (Voc), short circuit
currents (Jsc), fill factors (FF), and power conversion efficiencies
(PCE). At 1:2 weight ratio of polymer/PC71BM, the device with
PT-ID/PC71BM as active layer (70 nm) gave a Voc value of
0.87 V, a FF of 60%, and a Jsc value of 1.76 mA/cm2, resulted a
PCE value of 0.92%. The devices with PTT-ID/PC71BM as
active layer (65 nm) showed a Voc of 0.84 V, a Jsc of 3.90 mA/
cm2, and a FF of 53%, resulted a PCE of 1.74%. The devices with
PBDT-ID/PC71BM as active layer (80 nm) exhibited a Voc of
0.71 V, a Jsc of 7.93 mA/cm2, a FF of 34%, and a PCE of 1.91%.
The polymer PTT-ID containing device demonstrated a better
photovoltaic performance than the polymer PT-ID containing
device. The better performance of polymer PTT-ID than poly-
mer PT-ID may be attributed to the combined factors such
absorption, molecular weights and hole mobility. The open-
circuit voltages were related to the HOMO energy levels of
polymers. The polymer PT-ID1 had the lowest HOMO energy
level and the OPV device containing this polymer had the highest
Voc. The large branched side chains effectively improved the
solubility of the polymers. However, they might also greatly
reduce the crystallinty of polymer, thereby, resulted in low hole
mobility and low Jsc. The PBDT-ID possessed short branched
side chains and the devices showed a Jsc value as high as 7.93 mA/
cm2. It was significantly higher than that of PT-ID1 and PTT-
ID1 containing devices. The AFM imagines also showed that the
optical band gaps for large solar photon harvest. On the basis of
the systematic study and comprehensive consideration, ideal
polymer for OPV application was proposed before.13 It might
have a LUMO energy level of about -3.9 eV (0.3 eV higher than
those of PCBMs), a HOMO energy level of about -5.4 eV, and a
bandgap of about 1.5 eV for optimal performance. In many
aspects, these newly synthesized polymers closely resemble
the ideal low band gap polymers suggested by Scharber, Brabec,
and others in design rules of polymers for organic solar cell
applications.13b,14
Charge Transport in Polymer/PC71BM Blends. Hole-only
devices were fabricated with the configuration of ITO/PEDOT:
PSS/polymer (or polymer:PC71BM)/MoO3/Al. The hole mo-
bilities were measured by space charge limited current (SCLC)
method and were calculated by following equation:
!
rffiffiffi
9
V
V2
L3
J ¼ εε0μ exp γ
8
L
where J is the current density, V is the applied voltage, L is the
thickness of the active layer, μ is the mobility, ε is the dielectric
constant, ε0 is the permittivity of free space, and γ is the field-
activation factor.
Figure 3 showed the relationship between current and voltage
in the hole-only devices of polymer/PC71BM (1:2) blend films.
The calculated hole mobilities of PT-ID1/PC71BM, PTT-ID1/
PC71BM and PBDT-ID/PC71BM blend films were 1.30 ꢀ 10-8
,
2.35 ꢀ 10-7, and 1.07 ꢀ 10-5 cm2/(V s), respectively. The hole
mobilities of polymers were much lower than electron mobilities
of PCBMs (∼10-3 cm2/(V s)). The mismatch of charge
mobilities might be the key reason that limited the performance
of solar cell devices.
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Table 3. Photovoltaic Performances of PCS devices
polymer
polymer:PC71BM (w/w)
d (nm)
Voc (V)
Jsc (mA/cm2)
FF (%)
PCE (%)
PT-ID1
1:1
1:2
1:3
1:1
1:2
1:3
1:1
1:2
1:3
80
70
80
65
65
75
85
80
90
0.83
0.87
0.86
0.84
0.84
0.85
0.70
0.71
0.71
1.68
1.76
1.69
3.89
3.90
2.99
5.00
7.93
7.13
38
60
58
43
53
51
33
34
35
0.53
0.92
0.85
1.42
1.74
1.30
1.17
1.91
1.76
PTT-ID2
PBDT-ID
carried out. The moderate performance of isoindigo-based
polymer solar cell devices might result from unbalanced charge
carrier mobility in polymer/PCBM composite. Optimizations on
structures, molecular weights of polymer and morphologies of
composites for the improvement of hole mobility might result
balanced charge carrier mobility in active layer and further
enhance the performance OPV devices.
’ EXPERIMENTAL SECTION
Instrumentation. Nuclear magnetic resonance (NMR) spectra
were recorded on a Mercury plus 400 MHz machine. Gel permeation
chromatography (GPC) measurements were performed on a Waters
1515 series GPC coupled with UV-vis detector using tetrahydrofuran
as eluent with polystyrenes as standards. Thermogravimetric analyses
(TGA) were conducted with a TA Instruments QS000IR at a heating
rate of 20 °C min-1 under nitrogen gas flow. Differential scanning
calorimetry (DSC) analysis was performed on a TA Instruments
Q2000 in a nitrogen atmosphere. All the samples (about 10.0 mg in
weight) were heated up to 300 °C first and held for 2 min to remove
thermal history, followed by cooling at the rate of 20 °C/min to 20 °C
and then by heating at rate of 20 °C/min to 300 °C. UV-vis absorption
spectra were recorded on a Perkin-Elmer model λ 20 UV-vis spectro-
photometer. Electrochemical measurements were conducted on a CHI
600 electrochemical analyzer under nitrogen in a deoxygenated anhy-
drous acetonitrile solution of tetra-n-butylammonium hexafluorophos-
phate (0.1 M). A platinum electrode was used as a working electrode, a
platinum-wire was used as an auxiliary electrode, and an Ag/Agþ
electrode was used as a reference electrode. Thin film of polymer was
coated on the surface of platinum electrode and ferrocene was chosen as
a reference. The atomic force microscope (AFM) measurements were
performed on a SPA300HV instrument with a SPI3800 controller
(Seiko Instruments).
Device Fabrication and Characterization. Polymer solar cells
(PSCs) with the device structures of ITO/PEDOT:PSS/polymer:
PC71BM/LiF/Al were fabricated as follows: a ca. 40 nm-thick PEDOT:
PSS (Baytron P AI 4083) layer was spin-coated from an aqueous
solution onto the precleaned ITO substrates. The coated substrates
were dried at 120 °C for 30 min in air and were transferred into a
nitrogen filled glovebox. A film was spin-coated on top of the PEDOT/
PSS layer from a solution containing a mixture of polymer:PC71BM (1:2
weight ratio) in chlorobenzene. The samples were transferred into an
evaporator and 1 nm-thick of LiF layer and 100 nm-thick of Al layer with
area of 0.12 cm2 were thermally deposited under a vacuum of 10-6 Torr.
The devices were encapsulated in a glovebox and were measured in air.
Current-voltage characteristics were measured using a computer con-
trolled Keithley 236 source meter. The photocurrents were measured
under AM 1.5G illumination at 100 mW/cm2 from a solar simulator
(Oriel, 91160A-1000). Devices for space-charge-limited current
Figure 4. Current-voltage characteristics of solar cell devices under
illumination of AM 1.5 G, 100 mW/cm2.
film of PBDT-ID/PC71BM exhibited fine domains compared to
the film of PTT-ID2/PC71BM (Supporting Information, Figure
S4). The external quantum efficiency (EQE) curves of PSC
devices were shown in Figure S2 (Supporting Information). The
EQE measurements showed that the isoindigo-based devices
exhibited very broad photoresponse range from 300 to 800 nm.
PBDT-ID:PC71BM composite has higher EQE values compared
to PT-ID1:PC71BM and PTT-ID1:PC71BM. The EQE value of
PBDT-ID:PC71BM composite reached 30-40% in the range
350-630 nm. This contributed to the high Jsc value.
The moderate performance of isoindigo-based polymer
solar cell devices might be attributed to low hole motility of
the polymers. They were much lower than the electron
mobilities of PCBMs. The unbalanced charge carrier mobility
limited the performance of polymer solar cell devices. Opti-
mizations on structures, molecular weights of polymers and
morphologies of composites for the improvement of hole
mobility are in progress.
’ CONCLUSIONS
Isoindigo-based conjugated polymers with three different
donors have been synthesized. Isoindigo-based conjugated poly-
mers possess relatively low HOMO energy level for high open
circuit voltage, a suitable LUMO energy level for charge separa-
tion, and optimized optical band gap for polymer solar cell
applications. Isoindigo with its perfect planar π-conjugated
structure and electron deficient nature can be a useful new
monomer for construction of low band gap conjugated polymers.
Relative large branched side chains or multiple short branched
side chains are required to ensure the solubility of isoindigo based
polymers. Preliminary investigations on organic solar cell devices
with polymers as donors and PC71BM as acceptor were also
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ARTICLE
(SCLC) measurements were fabricated in a manner similar to the solar
cell devices with the structures of ITO/PEDOT:PSS/polymer:
PC71BM(1:2)/MoO3(10 nm)/Al.
Materials. 6-Bromoisatin and 6-bromooxindole were obtained
from Darui Chemical Co. Ltd., Shanghai, China. Other materials used
in this work were purchased from Sigma-Aldrich Chemical Co.,
Alfa Aesar Chemical Company and Sinopharm Chemical Reagent Co.
Ltd., China. Tetrahydrofuran (THF) and toluene were freshly distilled
over sodium wire under nitrogen prior to use.
Polymer PT-ID2. The same procedure was used as for polymer
PTT-ID1. Compoundsusedweretris(dibenzylideneacetone)dipalladium
(0.026 g, 0.029 mmol), triphenylarsine (0.035 g, 0.115 mmol), compound
3 (0.93 g, 1.44 mmol), compound 7 (0.59 g, 1.44 mmol), and toluene
(40 mL). The polymer was precipitated after heating at 110 °C for 5 h.
The precipitate was insoluble in any solvent.
’ ASSOCIATED CONTENT
S
Supporting Information. Text giving experimental sec-
Synthesis of Monomers and Polymers. The synthetic routes
for monomers and polymers are shown in Scheme 1 and Scheme 2.
1-Bromo-2-octyldodecane was synthesized according to the literature
methods.15 Compound 4 and 5 were synthesized in our previous work.11a
6,60-Dibromodi(2-octyldodecyl)isoindigo (2). 6,60-Dibromo-
isoindigo (2.0 g, 4.76 mmol) and potassium carbonate (3.3 g, 23.8 mmol)
were added to the solution of 1-bromo-2-octyldodecane (4.3 g, 11.9 mmol)
in dimethylformamide (60 mL). The mixture was reacted at 100 °C for
18 h, and then was cooled to room temperature. Water (100 mL) was
added and the mixture was extracted with dichloromethane. The com-
bined organic layer was dried with anhydrous sodium sulfate. Solvent was
removed under reduced pressure and residue was purified by flash
chromatography on silica gel with diethyl ether/hexane (1: 30) as eluent
to give a deep red solid (3.0 g, 64.2%). 1H NMR (CDCl3, 400 MHz, δ):
9.07 (d, J = 8.8Hz, 2H), 7.16 (m, 2H), 6.89 (d, J = 1.5 Hz, 2H), 3.62(d, J =
8.0 Hz, 4H), 1.82-1.94 (s, 2H), 1.20-1.40 (m, 64H), 0.83-0.90 (m,
12H). 13C NMR (CDCl3, 100 MHz, δ): 168.30, 146.41, 132.76, 131.24,
126.87, 125.30, 120.59, 111.74, 44.90, 36.30, 32.13, 32.08, 31.72, 30.20,
29.86, 29.84, 29.81, 29.76, 29.55, 29.50, 26.58, 22.91, 22.88, 14.32.
Polymer PTT-ID1. Tris(dibenzylideneacetone)dipalladium (0.015 g,
0.016 mmol) and triphenylarsine (0.019 g, 0.064 mmol) were added to a
solution of compound 2 (0.78 g, 0.79 mmol) and compound 6 (0.37 g, 0.79
mmol) in toluene (20 mL) under nitrogen. The solution was subjected to
three cycles of evacuation and admission of nitrogen. The mixture was
heated to 110 °C for 48 h. After cooled to room temperature, the mixture
was poured into methanol (100 mL) and was stirred for 2 h. A purple-blue
precipitate was collected by filtration. The product was purified by washing
with methanol and hexane in a Soxhlet extractor for 24 h each. It was
extracted with hot chloroform in an extractor for 24 h. After removing
solvent, a purple-blue solid was collected (0.55 g, 72.3%). 1H NMR
(CDCl3, 400 MHz, δ): 8.2-9.2 (br, 2H), 6.0-7.3 (br, 6H), 3.5-3.8
(br, 4H), 1.96-2.04 (br, 2H), 1.0-1.86 (br, 64H), 0.72-0.94 (br, 12H).
Mn = 37.6 kDa, PDI = 3.4.
b
tion, characterization, materials, and instrumentation and figures
showing TGA curves, EQE curves, AFM images, and NMR
spectra. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Authors
*E-mail: qz14@sjtu.edu.cn (Q.Z.); xiezy_n@ciac.jl.cn (Z.Y.X.).
’ ACKNOWLEDGMENT
This work was supported by National Nature Science Foun-
dation of China (NSFC Grant Nos. 20674049 and 20834005)
and Shanghai municipal government (Grant Nos. B202 and
10ZZ15).
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PTT-ID1. Compounds usedwere tris(dibenzylideneacetone)dipalladium
(0.013 g, 0.014 mmol), triphenylarsine (0.018 g, 0.056 mmol), compound
2 (0.71 g, 0.72 mmol), and compound 7 (0.30 g, 0.72 mmol). After work-
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1
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