Thieno-, furo-, and selenopheno[3,4-c ]pyrrole-4,6-dione copolymers: Effect of the heteroatom on the electrooptical properties

Article abstract of DOI:10.1021/ma3011894

New push-pull conjugated polymers based on furo[3,4-c]pyrrole-4,6-dione (FPD) and selenopheno[3,4-c]pyrrole-4,6-dione (SePD) have been synthesized and compared with their thieno[3,4-c]pyrrole-4,6-dione (TPD) analogues to investigate the effects of the heteroatom on the electrooptical properties. The copolymers were synthesized using either Stille cross-coupling or direct heteroarylation polymerization (DHAP), the latter method giving high molecular weights. Hypsochromic shifts of the band gaps were observed for FPD-based copolymers (sulfur substituted by oxygen) while small bathochromic shift was observed for SePD (sulfur substituted by selenium) when compared to its TPD analogue. These two new classes of conjugated polymers exhibit electrooptical properties that could lead to interesting bulk heterojunction plastic solar cells.

Full text of DOI:10.1021/ma3011894

Article
pubs.acs.org/Macromolecules
Thieno‑, Furo‑, and Selenopheno[3,4‑c]pyrrole-4,6-dione
Copolymers: Effect of the Heteroatom on the Electrooptical
Properties
Serge Beaupre, Agnieszka Pron, Simon H. Drouin, Ahmed Najari, Lauren G. Mercier, Amelie Robitaille,
́
́
and Mario Leclerc*
Canada Research Chair on Electroactive and Photoactive Polymers, Department of Chemistry, Universite
G1V 0A6, Canada
́
Laval, Quebec City, Quebec
S
* Supporting Information
ABSTRACT: New push−pull conjugated polymers based on furo[3,4-c]pyrrole-
4,6-dione (FPD) and selenopheno[3,4-c]pyrrole-4,6-dione (SePD) have been
synthesized and compared with their thieno[3,4-c]pyrrole-4,6-dione (TPD)
analogues to investigate the effects of the heteroatom on the electrooptical
properties. The copolymers were synthesized using either Stille cross-coupling or
direct heteroarylation polymerization (DHAP), the latter method giving high
molecular weights. Hypsochromic shifts of the band gaps were observed for FPD-
based copolymers (sulfur substituted by oxygen) while small bathochromic shift
was observed for SePD (sulfur substituted by selenium) when compared to its
TPD analogue. These two new classes of conjugated polymers exhibit
electrooptical properties that could lead to interesting bulk heterojunction plastic
solar cells.
s,36−38 poly(n-alkylselenophene)s,39−41 and poly(n-
alkylthiophene)s42 showed that the nature of the heteroatom
in the heterocycle may have a strong influence on their
solubility, intermolecular interactions, and optical and elec-
tronic properties. Therefore, we report the first synthesis of
new furo[3,4-c]pyrrole-4,6-dione (FPD) and selenopheno[3,4-
c]pyrrole-4,6-dione (SePD) derivatives where the sulfur atom
in the heterocycle of TPD has been replaced respectively by an
oxygen or a selenium atom. Copolymerizations of these new
pull moieties with carefully chosen push units were done using
either Stille cross-coupling reactions or direct heteroarylation
polymerization.35
1. INTRODUCTION
Harvesting the unlimited and renewable energy from sunlight
to produce electricity through photovoltaic devices is a
promising way to address growing global energy needs while
minimizing detrimental effects on the environment. Among all
photovoltaic technologies, polymer bulk heterojunction (BHJ)
solar cells offer a compelling option for tomorrow’s photo-
voltaic devices since they can be easily prepared using low-cost
and energy-efficient roll-to-roll manufacturing processes.1−9
During the past 5 years, development of new classes of
conjugated copolymers combined with optimization of device
fabrication led to significant improvements of the power
conversion efficiency of bulk heterojunction (BHJ) solar
cells.10−13 Lately, push−pull copolymers based on thieno[3,4-
c]pyrrole-4,6-dione (TPD) rose among the most efficient
materials for bulk heterojunction solar cells with power
conversion efficiency exceeding 8%.13−23 A lot of work has
been done in order to tune the band gap of push−pull TPD-
based copolymers by using several comonomers with different
electron-donating strength. One can think about carba-
zoles,24,25 bithiophenes,18,23,26 benzodithiophenes,14−16,22 cy-
clopentadithiophenes,27−30 dithienosiloles,17,19,31,32 and dithie-
nogermoles20,33 which led to copolymers with band gap ranging
from 1.5 to 2.2 eV. While long or branched side chains have
been added to TPD comonomers to promote the solubility of
the copolymers,34,35 tuning of the strength of the electron-
withdrawing behavior of the TPD moiety through chemical
modifications of the backbone has not been investigated yet.
Comparative studies between oligo- and poly(n-alkylfuran)-
2. RESULTS AND DISCUSSION
Monomers and Copolymers. The synthetic routes for
thieno[3,4-c]pyrrole-4,6-dione (TPD),14,23 furo[3,4-c]pyrrole-
4,6-dione (FPD), and selenopheno[3,4-c]pyrrole-4,6-dione
(SePD) comonomers are depicted in Schemes 1−4. Thieno-
[3,4-c]pyrrole-4,6-dione-based copolymers P1S and P4S
(Scheme 5) were prepared according to the literature and
used as benchmarks since these two push−pull copolymers are
among the most efficient materials in bulk heterojunction solar
cells with power conversion efficiencies of 7.1% and 7.3%,
respectively.18,22 Furan-3,4-dicarboxylic acid (5) was prepared
in high yield (97%) by the saponification of the commercially
Received: June 12, 2012
Revised: August 6, 2012
Published: August 28, 2012
© 2012 American Chemical Society
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a
14,23
,
Scheme 1. Synthesis of Thieno[3,4-c]pyrrole-4,6-dione (TPD) Comonomers
a
Reagents and conditions: (i) Ac2O, 140 °C, overnight; (ii) R−NH2, toluene, reflux 24 h; (iii) SOCl2, reflux, 12 h; (iv) NBS, H2SO4/CF3COOH, rt
overnight.
a
Scheme 2. Synthesis of Furo[3,4-c]pyrrole-4,6-dione (FPD) Comonomers
a
Reagents and conditions: (i) KOH, EtOH, reflux; (ii) oxalyl chloride, reflux; (iii) R−NH2, 140 °C, 2 h.
a
Scheme 3. Synthesis of 1,3-Dibromo-5-octylfuro[3,4-c]pyrrole-4,6-dione
a
Reagents and conditions: for the synthesis of compound 8, see Supporting Information. (i) KOH, EtOH, reflux; (ii) oxalyl chloride, reflux; (iii) n-
octylamine, 140 °C, 2 h.
tion, we developed a new synthetic route as shown in Scheme
3. Dimethyl 2,5-dibromofuran-3,4-dicarboxylate (8) was
prepared from furan in three steps according to reported
procedures (see Supporting Information).45 Saponification of
compound 8 led to 2,5-dibromo-furan-3,4-dicarboxylic acid (9)
(Scheme 3). Treatment of compound 9 with oxalyl chloride
gave 2,5-dibromo-furan-3,4-dicarbonyl dichloride (10). Then
2,5-dibromo-furan-3,4-dicarbonyl dichloride was reacted with
n-octylamine (in melted state) to afford 1,3-dibromo-5-
octylfuro[3,4-c]pyrrole-4,6-dione (11) which is suitable for
the Stille cross-coupling polymerization method. In parallel,
selenophene-3,4-dicarboxylic acid (12) was prepared in three
steps from commercially available selenophene (Scheme 4).46
5-Octyl-selenopheno[3,4-c]pyrrole-4,6-dione (13) was pre-
pared using a new synthetic procedure developed for the
synthesis of low-cost TPD comonomers.47 The diacid
precursor (12) and n-octylamine were mixed and reacted in
the melted state. This new synthetic route reduces the number
of chemical steps and avoids the need of two highly reactive
chemicals (thionyl chloride or oxalyl chloride) involved in the
synthesis of 5-alkylthieno[3,4-c]pyrrole-4,6-dione derivatives.14
Bromination of 5-octylselenopheno[3,4-c]pyrrole-4,6-dione
(13) using N-bromosuccinimide in a mixture of H2SO4/
trifluoroacetic acid successfully led to 1,3-dibromo-5-octyl-
selenopheno[3,4-c]pyrrole-4,6-dione (14).
Scheme 4. Synthesis of 5-Octylselenopheno[3,4-c]pyrrole-
4,6-dione (SePD)
a
a
Reagents and conditions: (i) n-octylamine, 200 °C; (ii) NBS, H2SO4/
CF3COOH, rt overnight.
available dimethyl-3,4-furan dicarboxylate (4) (Scheme 2).
Furan-3,4-dicarboxylic acid (5) was treated with oxalyl chloride
to obtain furan-3,4-dicarbonyl dichloride (6) according to a
known procedure.43 5-Alkylfuro-[3,4-c]pyrrole-4,6-dione (7a−
c) (FPD) comonomers (suitable for direct heteroarylation
polymerization (DHAP)) were prepared in low yields using the
melting state procedure reported for the synthesis of 1,3-
dibromo-5-octylthieno[3,4-c]pyrrole-4,6-dione.44 Bromination
at the 1,3-positions of 5-alkylfuro[3,4-c]pyrrole-4,6-dione
(7a−c), using classical bromination procedures (Br2, NBS,
DBI) failed and led to unwanted side reactions such as ring-
opening of the furan moiety. To circumvent stability issues of
5-alkylfuro[3,4-c]pyrrole-4,6-dione during bromination reac-
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Scheme 5. Stille Cross-Coupling Polymerization
Our previous work on thieno[3,4-c]pyrrole-4,6-dione-based
copolymers showed that direct heteroarylation polymerization
(DHAP) reduces significantly the number of chemical steps
and led to higher molecular weights when compared to
analogues made by Stille cross coupling polymerization.35 Stille
and DHAP polymerization methods were used for the synthesis
of several new push−pull copolymers (P1−P11) based on
promising push units (Figure 1) and the following pull
oarylation polymerization (DHAP), and we are working
actively on the reaction conditions optimization.
Molecular Weights. All polymers were characterized by
size exclusion chromatography (SEC) using monodisperse
polystyrene standard in hot 1,2,4-trichlorobenzene (TCB), and
data are summarized in Table 1. Direct heteroarylation
polymerization (DHAP) has proven to be a clean and efficient
polymerization for high molecular weight materials.35 After
careful optimization of the Stille polymerization parameters, we
found that the number-average molecular weight of P1S hit a
plateau at Mn = 20 kDa. On the other hand, direct
heteroarylation polymerization (DHAP) led to a higher
number-average molecular weight for P1H (Mn = 51 kDa).
The same enhancement of the molecular weights using DHAP
instead of Stille cross-coupling polymerization was observed for
P2S vs P2H and P4S vs P4H. Since molecular weights are known
to modulate the properties of conjugated polymers such as
solubility, crystallinity, and charge mobility, one can think that
P1H, P2H, and P4H would be promising materials for bulk
heterojunction solar cells. The versatility of the direct
heteroarylation polymerization (DHAP) method was demon-
strated by the synthesis of new push−pull conjugated polymers
(P5H−P11H). According to the data reported in Table 1, the
effect of the heteroatom (sulfur versus oxygen) on the DHAP
polymerization reaction is rather small. Indeed, most of the
TPD−FPD dyads had similar molecular weights. However, we
noticed that heteroatom (oxygen against sulfur) modify the
solubility of the resulting polymer. According to the literature,
it seems that oligofurans are more soluble than their
oligothiophene analogues.37 We noticed precipitation of P6H
(Mn = 10 kDa) during the polymerization reaction in hot
toluene while P7H (Mn = 16 kDa) remained in solution for the
entire polymerization time (24 h). Precipitation of polymers
during polymerization reaction prevents chain growth and
limits molecular weights. Finally, optimized polymerization
conditions23 of P8H (Mn = 41 kDa) led to higher molecular
weights than nonoptimized polymerization of P9H (Mn = 21
kDa), whereas P10H (Mn = 14 kDa) and P11H (Mn = 17 kDa)
have similar number-average molecular weights. However, as
Figure 1. Molecular structure of selected push comonomers.
moieties: (1) thieno[3,4-c]pyrrole-4,6-dione (TPD), (2) furo-
[3,4-c]pyrrole-4,6-dione (FPD), and (3) selenopheno[3,4-
c]pyrrole-4,6-dione (SePD). The synthetic routes are shown
in Schemes 5 and 6 while the molecular structures of the
polymers studied are summarized in Figure 2. Up to now, we
failed to get reproducible and defect-free selenopheno[3,4-
c]pyrrole-4,6-dione-based copolymers (SePD) by direct heter-
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a
Scheme 6. Direct Heteroarylation Polymerization (DAHP)
a
Reagents and conditions: (i) trans-di(μ-acetato)-bis[o-(di-o-tolylphosphino)benzyl]dipalladium(II) (4 mol %), tris(o-methoxyphenyl)phosphine (8
mol %), Cs2CO3 (2 equiv), pivalic acid (30% mol), dry toluene, 120 °C, 24−36 h.
mentioned above, the FPD-based copolymers were found to be
more soluble than their TPD analogues.
materials. UV−vis spectra of P1S, P2S, and P3S are shown in
Figure 4a, and the effect of the heteroatom (rather small) on
the optical properties can be seen. The substitution of the sulfur
atom (P1S) by oxygen (P2S) led to a hypsochromic shift of
both the maximum of absorption (24 nm) and the band gap
(0.10 eV). According to the literature, the furan ring is smaller
than the thiophene ring due to the smaller size and higher
electronegativity of the oxygen atom.37 The lone electron pairs
are more localized on the oxygen atom than on the sulfur atom,
which makes furan less aromatic than thiophene.37 Moreover,
the C−O bond (1.362 Å) is smaller than the the C−S bond
(1.714 Å). Since n-alkylfuro[3,4-c]pyrrole-4,6-dione (FPD) and
n-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) are, from a
chemical point of view, substituted furans and thiophenes,
one can think that FPD derivatives may be weaker pull moieties
when compared to their TPD counterparts, resulting in higher
band gaps for push−pull FPD-based copolymers. Indeed, the
optical band gap of P2S (Egopt = 1.90 eV) is larger than P1S
(Egopt = 1.80 eV). A noticeable increase of the oxidation
potential for P2S was also observed compared to P1S (see
Supporting Information), resulting in a stabilization of the
Optical Properties and Electronic Properties. The
electrooptical properties of all copolymers are summarized in
Table 2. Despite relatively large optical band gaps (ranging
from 1.77 to 1.97 eV), all polymers have broad UV−vis
absorption spectra which is of paramount importance for
efficient absorption of solar spectral flux in bulk heterojunction
solar cells. The effect of the heteroatom (sulfur, oxygen, and
selenium) on the optical properties of [3,4-c]pyrrole-4,6-dione
was studied by comparing TPD- to FPD- and SePD-based
copolymers. The effect of molecular weights on the optical
properties is negligible since they are all within the same range,
except for P1 and P2. As reported in Table 1, we found that
direct heteroarylation polymerization led to higher molecular
weights than Stille cross-coupling polymerization. UV−vis
spectra of P1S vs P1H and P2S vs P2H are shown in Figure
3a,b. One can see similarities between UV−vis spectra of both
low- and high-molecular-weight polymers. The saturation of the
optical properties means that the effective conjugation length
was already reached for the so-called low-molecular-weight
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the LUMO energy level.48 We found that the effect of the
selenium (P3H) on the electro-optical properties is rather small.
We noticed a bathochromic shift of the maximum of absorption
(25 nm) and a small reduction of the band gap (0.03 eV) for
P3S when compared to P1S (Figure 4a). Unlike polyseleno-
phene/polythiophene analogues, no stabilization of the LUMO
level was observed for SePD copolymers (Table 2). Since the
electronegativity of sulfur (2.58) and selenium (2.55) are
almost identical, one can think that SePD and TPD have the
same pull strength. A full evaluation and optimization of bulk
heterojunction solar cells is in progress for all polymers.
3. CONCLUSION
We have studied the electrooptical properties of several new
push−pull conjugated polymers obtained by Stille cross-
coupling or direct heteroarylation polymerization. Our new
pull moieties are closely related to thieno[3,4-c]pyrrole-4,6-
dione derivatives, and the effect of the heteroatom (sulfur,
oxygen, and selenium) on the electrooptical properties was
investigated. For the first time, furo[3,4-c]pyrrole-4,6-dione
(FPD) and selenopheno[3,4-c]pyrrole-4,6-dione (SePD) de-
rivatives were synthesized and successfully polymerized with
some of the most studied push units. We noticed that the FPD
copolymers are more soluble than their TPD and SePD
analogues, but the effects of the heteroatom on the electro-
optical properties are rather small. However, some TPD- and
FPD-based copolymers prepared by direct heteroarylation
polymerization (DHAP) have high molecular weights, broad
absorption spectra, reduced band gaps, and deep HOMO/
LOMO energy levels which make them suitable as active
components in bulk heterojunction solar cells. Optimization of
the direct heteroarylation polymerization method and evalua-
tion of these new materials in bulk heterojunction solar cells are
in progress.
Figure 2. Molecular structure of push−pull copolymers.
Table 1. Characterization of Polymers
4. EXPERIMENTAL SECTION
a
b
b
b
polymer
yield (%)
Mn (kDa)
Mw (kDa)
PDI
Instrumentation. 1H and 13C NMR spectra were recorded using a
Varian Inova 400 MHz or Bruker AC 300 MHz in deuterated
chloroform at 298 K. Number-average (Mn) and weight-average (Mw)
molecular weights were determined by size exclusion chromatography
(SEC) using a high-temperature Varian Polymer Laboratories
GPC220 equipped with an RI detector and a PL BV400 HT bridge
viscometer. The column set consists of 2 PLgel Mixed C (300 × 7.5
mm) columns and a PLgel Mixed C guard column. The flow rate was
fixed at 1.0 mL/min using 1,2,4-trichlorobenzene (TCB) (with
0.0125% BHT w/v) as eluent. The temperature of the system was
set to 110 °C. The samples were prepared at concentration of
nominally 1.0 mg/mL in hot TCB. Dissolution was performed using a
Varian Polymer Laboratories PL-SP 260VC sample preparation
system. The sample vial was held at 110 °C with stirring for 1 h for
complete dissolution. The solution was filtered through a 2 μm porous
stainless steel filter into a 2 mL chromatography vial. The calibration
method used to generate the reported data was the classical
polystyrene method using polystyrene narrow standards dissolved in
TCB. UV−vis−NIR absorption spectra were recorded using a Varian
Cary 500 UV−vis−NIR spectrophotometer with path length quartz
cells of 1 cm. Spin-coated films on glass plates were used for solid-state
UV−vis−NIR measurements. Optical bandgaps were determined from
the onset of the absorption band (solid state). Cyclic voltammograms
(CV) (see Supporting Information) were recorded on a Solartron
1287 potentiostat using platinum wires as working electrode and
counter electrode at a scan rate of 50 mV/s. A film of polymer was
deposited on the working electrode. The reference electrode was Ag/
Ag+ (0.01 M of AgNO3 in acetonitrile), and the electrolyte was a
solution of 0.1 M of tetrabutylammonium tetrafluoborate in dry
P1S
P1H
P2S
P2H
P3S
P4S
P4H
P5H
P6H
P7H
P8H
P9H
P10H
P11H
98
65
95
78
93
84
38
62
49
79
94
83
83
51
20
51
11
18
13
12
18
15
10
16
41
21
14
17
47
145
21
39
30
17
28
27
14
27
95
55
25
27
2.4
2.9
1.9
2.2
2.3
1.4
1.6
1.7
1.4
1.7
2.3
2.6
1.8
1.6
a
S: Stille cross-coupling polymerization; H: direct heteroarylation
polymerization determined by SEC in hot TCB (110 °C) using
polystyrene standards.
b
HOMO energy level of 0.09 eV for P2S vs P1S. As shown in
Table 2, for most TDP/FPD copolymers pairings, a
hypsochromic shift of the optical band gap and a stabilization
of the HOMO energy level for FPD-based copolymers were
observed (Figure 4b). On the other hand, it has been shown
that the incorporation of heavier atom such as selenium into
polythiophene narrows the band gap due to a stabilization of
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Table 2. Optical and Electrochemical Properties of Polymers
optical properties
electrochemical properties
a
b
c
d
polymer
λmax solution (nm)
λmax film (nm)
λonset film (nm)
Egopt (eV)
HOMO (eV)
LUMO (eV)
Egcv (eV)
P1S
P1H
P2S
P2H
P3S
P4S
P4H
P5H
P6H
P7H
P8H
P9H
P10H
P11H
550, 610
550, 610
533, 581
538, 586
565, 635
468
550, 610
550, 610
533, 581
538, 586
565, 635
556, 634
568, 630
550
685
685
652
645
700
700
683
640
691
657
677
643
685
630
1.80
1.80
1.90
1.92
1.77
1.77
1.81
1.94
1.80
1.89
1.83
1.93
1.81
1.97
5.56
5.56
5.65
5.65
5.51
5.64
5.68
5.76
5.56
5.54
5.66
5.65
5.64
5.80
3.75
3.75
3.79
3.79
3.75
3.97
3.81
3.81
3.73
3.75
3.86
3.80
3.83
3.84
1.81
1.81
1.86
1.86
1.76
1.71
1.87
1.95
1.83
1.79
1.80
1.85
1.81
1.96
468
500
477
580, 632
550, 600
562, 620
550, 600
568, 622
535, 582
550, 600
483
500
530, 604
535, 582
a
b
c
d
S: Stille cross-coupling polymerization; H: direct heteroarylation polymerization Dissolved in CHCl3 or o-DCB. Spin-coated films. Calculated
from the absorption edge wavelength of films.
Figure 3. Effect of the molecular weights on absorption spectra of (a) P1S vs P1H and (b) P2S vs P2H.
acetonitrile. In these conditions, the oxidation potential of ferrocene
was 0.09 V versus Ag/Ag+, whereas the oxidation potential of
ferrocene was 0.41 V versus SCE. The HOMO and LUMO energy
levels were determined from the oxidation and reduction onsets
(where the current differs from the baseline) assuming that SCE
electrode is −4.7 eV from vacuum.
purchased from Aldrich. Thieno[3,4-c]pyrrole-4,6-dione comonomers
(2a−c; 3a−c),14,23 furan-3,4-dicarboxylic acid (5),43 furan-3,4-
dicarbonyl dichloride (6),43 dimethyl 2,5-dibromofuran-3,4-dicarbox-
ylate (8),45 selenophene-3,4-dicarboxylic acid (12),46 2,6-bis-
(trimethyltin)-4,8-di(2-ethylhexyloxyl)benzo[1,2-b:3,4-b]dithiophene
(15),14 (4,4′-didodecyl-2,2′-bithiophene-5,5′-diyl)bis-
(trimethylstannane) (16),18 2,6-dibromo-4,8-di(2-ethylhexyloxyl)-
benzo[1,2-b:3,4-b]dithiophene (17),49 5,5′-dibromo-4,4′-didodecyl-
Chemicals. Thiophene-3,4-dicarboxylic acid (1) was purchased
from Frontier Scientific Inc. Dimethyl furan-3,4-dicarboxylate (4) was
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Figure 4. Effect of the heteroatom on optical properties of (a) P1S, P2S, and P3S and (b) P8H vs P9H.
2,2′-bithiophene (18),18 5,5″-dibromo-4,4″-didodecyl-2,2′;5′,2″-ter-
thiophene (19),23 and 2,6-dibromo-3,5-didodecylbisthieno[3,2-
b:2′,3′-d]thiophene (20)50 were prepared according to the literature.
Tetrahydrofuran was distilled over sodium/benzophenone system.
Toluene and acetonitrile were distilled over calcium hydride before
use.
(eluent DCM/hexane 2:1) to afford 1.10 g (Y = 34%) of the title
compound as white solid; mp 82−84 °C. 1H NMR (300 MHz, CDCl3,
ppm) δ: 7.75 (s, 2H); 3.48 (d, 2H, J = 7.3 Hz); 1.78 (m, 1H); 1.32 (m,
8H); 0.89 (m, 6H). 13C NMR (75 MHz, CDCl3, ppm) δ: 161.94;
138.60; 122.39; 42.41; 38.01; 30.43; 28.39; 23.78; 22.92; 13.94; 10.32.
Elemental analysis calculated as C14H19N1O3: C, 67.45; H, 7.68; N,
5.62; found: C, 67.50; H; 7.72; N, 5.63. HRMS: calculated (MNa+):
272.1257; found: 272.1259.
Synthesis of 5-(Octyl)furo[3,4-c]pyrrole-4,6-dione (7a). A
mixture of n-octylamine (0.46 mL, 2.7 mmol) and furan-3,4-dicarbonyl
dichloride (0.51 g, 2.6 mmol) was heated to 140 °C for 2 h. The
mixture was cooled down to room temperature. Ethyl acetate was
added, and the organic layer was washed with saturated sodium
carbonate (2×). The organic layer was dried over sodium sulfate and
filtered. The solvent was removed under reduced pressure, and the
residue was purified by flash chromatography on silica gel (eluent
DCM/hexane 2:1) to afford 0.27 g (Y = 34%) of the title compound as
Synthesis of 5-(9-Heptadecanyl)furo[3,4-c]pyrrole-4,6-dione
(7c). A mixture of heptadecan-9-amine (3.44 g, 13.5 mmol) and furan-
3,4-dicarbonyl dichloride (2.47 g, 12.8 mmol) was heated to 140 °C
for 2 h. The mixture was cooled down to room temperature. Ethyl
acetate was added, and the organic layer was washed with saturated
sodium carbonate (2×). The organic layer was dried over sodium
sulfate and filtered. The solvent was removed under reduced pressure,
and the residue was purified by flash chromatography on silica gel
(eluent DCM/hexane 2:1) to afford 1.12 g (Y = 23%) of the title
1
white solid; mp 111−113 °C. H NMR (300 MHz, CDCl3, ppm) δ:
7.75 (s, 2H); 3.58 (t, 2H, J = 7.3 Hz); 1.62 (m, 2H); 1.29 (m, 10H);
0.87 (t, 3H, J = 7.4 Hz). 13C NMR (75 MHz, CDCl3, ppm) δ: 161.70;
138.60; 122.48; 38.58; 31.72; 29.10 (2C); 28.33; 26.80; 22.57; 13.99.
Elemental analysis calculated as C14H19N1O3: C, 67.45; H, 7.68; N,
5.62. Found: C, 67.96; H; 7.96; N, 5.54. HRMS: calculated: 249.1365;
found: 249.1371.
1
compound as off-white solid; mp 32−33 °C. H NMR (300 MHz,
CDCl3, ppm) δ: 7.73 (s, 2H); 4.08 (m, 1H,); 2.02 (m, 2H); 1.62 (m,
2H); 1.22 (m, 24H,); 0.88 (t, 3H, J = 7.3 Hz). 13C NMR (75 MHz,
CDCl3, ppm) δ: 162.09; 138.47; 122.23; 52.75; 32.09; 31.79; 29.42;
29.24; 29.17; 26.61; 22.61; 14.03. Elemental analysis calculated as
C23H37N1O3: C, 73.56; H, 9.93; N, 3.73; found: C, 73.95; H; 10.26; N,
3.68. HRMS (MNa+): calculated: 398.2671; found: 398.2671.
Synthesis of 5-(2-Ethylhexyl)furo[3,4-c]pyrrole-4,6-dione
(7b). A mixture of 2-ethylhexylamine (2.2 mL, 13.6 mmol) and
furan-3,4-dicarbonyl dichloride (2.50 g, 12.9 mmol) was heated to 140
°C for 2 h. The mixture was cooled down to room temperature. Ethyl
acetate was added, and the organic layer was washed with saturated
sodium carbonate (2×). The organic layer was dried over sodium
sulfate and filtered. The solvent was removed under reduced pressure,
and the residue was purified by flash chromatography on silica gel
Synthesis of 2,5-Dibromofuran-3,4-dicarboxylic Acid (9). A
mixture of dimethyl 2,5-dibromofuran-3,4-dicarboxylate (5) (0.600 g,
1.8 mmol) and potassium hydroxide (0.369 g, 6.6 mmol) in ethanol
(44 mL) was stirred and heated at reflux for 3 h. The mixture was
cooled to room temperature and concentrated under reduced pressure
to leave a solid which was dissolved in water. The resulting solution
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Macromolecules
Article
was acidified to pH = 1 with aqueous HCl (6 M) and then saturated
with sodium chloride prior to extraction with ethyl acetate (2 × 100
mL). The organic extracts were combined and dried over magnesium
sulfate and filtered, and the solvent was removed under reduced
pressure to afford 0.49 g (Y = 89%) of the title product as an off-white
solid; mp 199−200 °C. 13C NMR (75 MHz, CDCl3, ppm) δ: 161.57,
130.75, 119.25. Elemental analysis calculated as C6H2Br2O5: C, 22.96;
H, 0.64; found: C, 22.94; H; 0.63. HRMS (MH+): calculated:
311.8269; found: 311.8275.
Synthesis of 2,5-Dibromofuran-3,4-dicarbonyl Dichloride
(10). Oxalyl chloride (6.5 mL, 76.5 mmol) was slowly added to 2,5-
dibromofuran-3,4-dicarboxylic acid (0.400 g, 1.3 mmol). The mixture
was heated to reflux for 2 h and then cooled to room temperature. The
volatiles were removed under reduced pressure, and the product was
used without any further purification.
Synthesis of 1,3-Dibromo-5-(octyl)furo[3,4-c]pyrrole-4,6-
dione (11). A mixture of n-octylamine (0.25 mL, 1.4 mmol) and
2,5-dibromofuran-3,4-dicarbonyl dichloride (0.447 g, 1.27 mmol) was
heated to 140 °C for 1 h. The mixture was cooled down to room
temperature. Ethyl acetate was added, and the organic layer was
washed with saturated sodium carbonate. The organic layer was dried
over sodium sulfate and filtered. The solvent was removed under
reduced pressure, and the residue was purified by flash chromatog-
raphy on silica gel (eluent DCM/hexane 2:1) to afford 0.14 g (Y =
27%) of the title compound as white solid; mp 113−115 °C. 1H NMR
(300 MHz, CDCl3, ppm) δ: 3.58 (t, 2H, J = 7.3 Hz); 1.62 (m, 2H);
1.29 (m, 10H); 0.87 (t, 3H, J = 7.4 Hz). 13C NMR (75 MHz, CDCl3,
ppm) δ: 159.46; 123.87; 120.25; 38.97; 31.76; 29.10 (2C); 28.24;
26.77; 22.62; 14.07. HRMS: C14H17Br2NO3: calculated: 407.9628;
found: 407.9625.
Synthesis of 5-(Octyl)selenopheno[3,4-c]pyrrole-4,6-dione
(13). n-Octylamine (0.114 g, 0.88 mmol) was added to seleno-
phene-3,4-dicarboxylic acid (0.175 g, 0.80 mmol). The reaction
mixture was stirred and heated to 200 °C over the span of 40 min.
Then the mixture is reacted at 200 °C for an additional 20 min and
then cooled down, diluted with dichloromethane (20 mL), and
concentrated under reduced pressure. The crude solid product was
purified by column chromatography using dichloromethane as the
eluent to afford 0.23 g (Y = 84%) of a beige solid; mp 107−108 °C. 1H
NMR (400 MHz, CDCl3, ppm) δ: 8.62 (s, 2H); 3.59 (t, 2H, J = 7.3
Hz); 1.67−1.60 (m, 2H); 1.31−1.25 (m, 10H); 0.87 (t, 3H, J = 6.7
Hz). 13C NMR (100 MHz, CDCl3, ppm) δ: 163.15; 138.59; 132.15;
38.59; 31.78; 29.17 (2C); 28.38; 26.89; 22.63; 14.09. HRMS:
C14H19N1O2Se1: calculated: 313.0589; found: 313.0589.
trimethyltin phenyl was added and reacted for 1 h to complete the
end-capping procedure. The whole mixture was cooled to room
temperature and poured in methanol, and the solid was recovered by
filtration. The polymers were purified by Soxhlet extraction using
acetone and then hexane. The polymers were then extracted with
chloroform. The solvent was reduced to about 10−15 mL, and the
mixture was poured into cold methanol. Polymers were recovered by
filtration.
General Procedure for Direct Heteroarylation Polymer-
ization. Dibromo comonomers (17−20) (0.1 mmol), 5-alkylthieno-
[3,4-c]pyrrole-4,6-dione (2a,b), or 5-alkylfuro[3,4-c]pyrrole-4,6-dione
(7a−c) (0.1 mmol), trans-di(μ-acetato)-bis[o-(di-o-tolylphosphino)-
benzyl]dipalladium(II) (4 mol %), tris(o-methoxyphenyl)phosphine
(8 mol %), Cs2CO3 (2 equiv), and pivalic acid (30% mol) were put in
microwave vial (2−5 mL). The vial was carefully sealed and put under
vacuum for 1 h. The solids were dissolved in dry and oxygen-free
toluene ([ ] = 0.2 M). The system was purged three times by vacuum/
argon cycling. The mixture was heated to 120 °C using an oil bath
equipped with a temperature controller. After 24−36 h, the polymer
was end-capped. The whole mixture was cooled to room temperature
and poured in methanol, and the solid was recovered by filtration. The
polymers were purified by Soxhlet extraction using acetone and then
hexane. The polymers were then extracted with chloroform. The
solvent was reduced to about 10−15 mL, and the mixture was poured
into cold methanol. Polymers were recovered by filtration.
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis of dimethyl 2,5-dibromofuran-3,4-dicarboxylate;
NMR spectra of FPD and SePD comonomers; cyclic
voltammograms of P1−P11. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: Mario.Leclerc@chm.ulaval.ca.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by grants from NSERC Photovoltaic
■
Innovation Network and by the Ministe′re du Dev
́
eloppement
Synthesis of 1,3-Dibromo-5-(octyl)selenopheno[3,4-c]-
pyrrole-4,6-dione (14). 5-Octylselenopheno[3,4-c]pyrrole-4,6-
dione (0.050 g, 0.16 mmol) was dissolved in sulfuric acid (0.20 mL)
and trifluoroacetic acid (0.65 mL). The reaction mixture was stirred in
the dark, and N-bromosuccinimide (0.090 g, 0.50 mmol) was added in
small portions. The mixture was stirred overnight at room temper-
ature. Then, cold water (2 mL) was added, and the resulting mixture
was extracted with dichloromethane (3 × 5 mL). The combined
organic layers were dried with anhydrous MgSO4, filtered, and
concentrated under reduced pressure. The crude product was purified
by column chromatography using ethyl acetate/hexanes (1:9) as the
eluent to afford 0.06 g (Y = 80%) as an orange solid; mp 129−130 °C.
1H NMR (400 MHz, CDCl3, ppm) δ: 3.57 (t, 2H, J = 7.3 Hz); 1.67−
́
Economique, de l’Innovation et de l’Exportation (MDEIE).
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