Furan containing diketopyrrolopyrrole copolymers: Synthesis, characterization, organic field effect transistor performance and photovoltaic properties

Article abstract of DOI:10.1039/c2jm14989c

In this work, we report design, synthesis and characterization of solution processable low band gap polymer semiconductors, poly{3,6-difuran-2-yl-2,5-di(2- octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-phenylene} (PDPP-FPF), poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1, 4-dione-alt-naphthalene} (PDPP-FNF) and poly{3,6-difuran-2-yl-2,5-di(2- octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-anthracene} (PDPP-FAF) using the furan-containing 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DBF) building block. As DBF acts as an acceptor moiety, a series of donor-acceptor (D-A) copolymers can be generated when it is attached alternatively with phenylene, naphthalene or anthracene donor comonomer blocks. Optical and electrochemical characterization of thin films of these polymers reveals band gaps in the range of 1.55-1.64 eV. These polymers exhibit excellent hole mobility when used as the active layer in organic thin-film transistor (OTFT) devices. Among the series, the highest hole mobility of 0.11 cm ² V^-1 s^-1 is achieved in bottom gate and top-contact OTFT devices using PDPP-FNF. When these polymers are used as a donor and [70]PCBM as the acceptor in organic photovoltaic (OPV) devices, power conversion efficiencies (PCE) of 2.5 and 2.6% are obtained for PDPP-FAF and PDPP-FNF polymers, respectively. Such mobility values in OTFTs and performance in OPV make furan-containing DBF a very promising block for designing new polymer semiconductors for a wide range of organic electronic applications.

Full text of DOI:10.1039/c2jm14989c

View Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2012, 22, 4425
www.rsc.org/materials
PAPER
Furan containing diketopyrrolopyrrole copolymers: synthesis,
characterization, organic field effect transistor performance and
photovoltaic properties†
a
ad
a
ab
a
Prashant Sonar,* Samarendra P. Singh, Evan L. Williams, Yuning Li,* Mui Siang Soh
ac
and Ananth Dodabalapur*
Received 4th October 2011, Accepted 23rd November 2011
DOI: 10.1039/c2jm14989c
In this work, we report design, synthesis and characterization of solution processable low band gap
polymer semiconductors, poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-
dione-alt-phenylene} (PDPP-FPF), poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]
pyrrole-1,4-dione-alt-naphthalene} (PDPP-FNF) and poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-
pyrrolo[3,4-c]pyrrole-1,4-dione-alt-anthracene} (PDPP-FAF) using the furan-containing 3,6-di(furan-
2
-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DBF) building block. As DBF acts as an acceptor
moiety, a series of donor–acceptor (D–A) copolymers can be generated when it is attached alternatively
with phenylene, naphthalene or anthracene donor comonomer blocks. Optical and electrochemical
characterization of thin films of these polymers reveals band gaps in the range of 1.55–1.64 eV. These
polymers exhibit excellent hole mobility when used as the active layer in organic thin-film transistor
2
ꢀ1 ꢀ1
(
OTFT) devices. Among the series, the highest hole mobility of 0.11 cm V
gate and top-contact OTFT devices using PDPP-FNF. When these polymers are used as a donor and
70]PCBM as the acceptor in organic photovoltaic (OPV) devices, power conversion efficiencies (PCE)
s
is achieved in bottom
[
of 2.5 and 2.6% are obtained for PDPP-FAF and PDPP-FNF polymers, respectively. Such mobility
values in OTFTs and performance in OPV make furan-containing DBF a very promising block for
designing new polymer semiconductors for a wide range of organic electronic applications.
1
. Introduction
choice for designing new high performance organic semi-
conductors due to enhanced charge transport through D–A
25,26
Recently, polymer semiconductors containing diketopyrrolo-
pyrrole (DPP) units in the main conjugated backbone have
emerged as a promising class of materials for OTFTs and OPV
intra- and intermolecular interactions.
The DPP unit also has
several other beneficial attributes including its planarity, strong
electron withdrawing capability and highly conjugated lactam
27
1–22
devices.
DPP is a strong electron acceptor (A) moiety and
structure which induces strong p–p interaction. Our group has
when pairing with electron donor (D) blocks, it can form push–
pull (or D–A) copolymers. Such copolymers allow for the
hybridization of the highest occupied molecular orbital (HOMO)
of the donor with the lowest unoccupied molecular orbital
recently designed and synthesized several solution processable
D–A copolymer semiconductors based on a 3,6-di(thiophen-2-yl)
pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DBT) block and these
materials have exhibited high performance in both OTFTs and
OPV due to their high charge carrier mobility and broad
(
LUMO) of the acceptor which results in delocalization of p
electrons and the formation of quinoidal structures causing
5–9
absorption spectra. DBT has proved to be a promising planar
23,24
a reduction in the band gap.
Such a D–A system is a popular
moiety due to minimal steric repulsions of thiophene with the
DPP core; the DBT block achieves a high degree of coplanarity
in the polymer backbone when combining it with other aromatic
blocks such as thiophene, bithiophene, thienothiophene, naph-
thalene and benzothidiazoles. Such a high coplanarity is
favourable for efficient charge transport properties and stronger
D–A interactions along the conjugated backbone. Thiophene,
selenophene, furan, and pyrrole are important five-membered
a
Institute of Materials Research and Engineering (IMRE), Agency for
3 Research Link,
Science, Technology, and Research (A*STAR),
Singapore 117602. E-mail: sonarp@imre.a-star.edu.sg
b
Department of Chemical Engineering, University of Waterloo, 200
University Avenue West, Waterloo, Ontario, Canada N2L 3G1. E-mail:
yuning.li@uwaterloo.ca
c
Microelectronics Research Centre, The University of Texas at Austin,
Austin, TX, 78758, USA. E-mail: ananth.dodabalapur@engr.utexas.edu
28
d
aromatic heterocycles for designing and synthesizing novel
organic semiconductors. Among them, thiophene is one of the
most studied heterocyclic compounds for organic electronic
Shiv Nadar University, Greater Noida, India
†
1
Electronic supplementary information (ESI) available. See DOI:
0.1039/c2jm14989c
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4425–4435 | 4425

View Online
applications but fewer studies have been done on furan con-
synthesis, optical and electrochemical characterization, device
performance (OTFT and OPV), and structure–property corre-
lation of these new copolymers are described.
29–33
taining materials for OTFT and OPV applications.
Recently,
oligofuran compounds have been used as the active component
34
in OTFTs. Additionally, furan based organic dyes have been
35
used for dye-sensitized solar cells. Furan-based heterocycles
2. Results and discussion
have also been used as an end group of small molecules in high
36
performance OPV devices. Interestingly, furan derivatives
exhibit similar energy levels and a comparable degree of
aromaticity in comparison to their thiophene counterparts.
Importantly, furan derivatives can be obtained from biomass
2
.1 Syntheses and characterization
The synthetic approach for making furan containing DPP
compound 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (DBF) (2) is outlined in Scheme 1. Compound 2 was
synthesized in 61% yield by reacting 2-furylnitrile (1) with dii-
sopropyl succinate in the presence of sodium tert-amyl alcohol
34
and considered ‘‘green’’ electronic materials. In this regard,
there is a growing interest in using furan as an alternative to other
commonly used heterocycles in the design of novel organic
semiconductors.
ꢁ
and iron chloride at 110 C, which is similar to the synthesis of
3
,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
In our study, we replaced the thiophene unit in DBT with
furan to form 3,6-di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4
(
DBT). In order to provide good solubility of the polymer, an
octyldodecyl group was introduced on the DPP core. Specifi-
(
2H,5H)-dione (DBF) and used this building block for synthe-
cally, the nitrogen atoms of compound 2 were alkylated by using
sizing D–A copolymers. Our group has recently reported DBF
and bithiophene based D–A polymer, [poly{3,6-difuran-2-yl-2,5-
di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-bithio-
phene}] PDBFBT, which exhibits a hole mobility of up to 1.54
2
-octyldodecyl bromide in anhydrous dimethylformamide
(
DMF) solvent in the presence of potassium carbonate (K CO ),
2
3
producing 2,5-bis(2-octyldodecyl)-3,6-di(furan-2-yl)pyrrolo[3,4-
c]pyrrole-1,4(2H,5H)-dione (3) in 48% yield. Bromination of
compound 3 was then carried out using bromine in chloroform
solvent at room temperature to afford 3,6-bis(5-bromofuran-2-
yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (4) in 58% yield after purification with column chroma-
tography. Compound 4 was used as a common block for poly-
merization with the bisboronic esters of phenylene, naphthalene
2
ꢀ1 ꢀ1
cm V s , the highest among reported furan based organic
9
semiconductors. In this work, we present the synthesis and
detailed characterization of three low band gap copolymer
semiconductors which are prepared from the combination of the
DBF acceptor unit with three commonly used electron donating
acene blocks (phenylene, naphthalene and anthracene) via
Suzuki coupling. The main intention of designing this series of
D–A copolymers is to study the effect of conjugated acenes (from
shorter to longer ones) on optical, electrochemical and device
performance properties. The donor units adjacent to the DBF
unit in this series of copolymers have been selected in such a way
that the polymer semiconductors can exhibit wide absorbance
and a band gap between 1.50 and 1.70 eV. We intentionally
introduced octyldodecyl as a long branched alkyl chain on both
sides of the nitrogen atom of the DBF unit for better solution
processability. These copolymers are soluble in common organic
solvents (e.g., chloroform, toluene, chlorobenzene, etc.) and can
be processed easily for making thin film organic electronic
devices. These materials were characterized by nuclear magnetic
resonance spectroscopy (NMR), gel permeation chromato-
graphy (GPC), UV-Vis absorption and photoluminescence (PL)
spectroscopy, thermogravimetric analysis (TGA) and cyclic
voltammetry (CV). OTFTs fabricated from all copolymers
exhibited p-channel performance with high mobility. OTFT
devices having poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyr-
rolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene} (PDPP-FNF) thin
1
13
C
and anthracene, respectively. Synthesis details with H and
NMR spectra of the respective intermediates and starting
comonomers are provided in the ESI†.
The synthetic route of three novel alternating copolymers poly
{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-
1,4-dione-alt-phenylene} (PDPP-FPF), poly{3,6-difuran-2-yl-
2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naph-
thalene} (PDPP-FNF) and poly{3,6-difuran-2-yl-2,5-di(2-octyl-
dodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-anthracene}
(
PDPP-FAF) comprising the DBF unit and phenylene, naph-
thalene and anthracene, respectively, is shown in Scheme 2.
2
film on an octyltrichlorosilane (OTS) treated Si/SiO substrate
2
ꢀ1 ꢀ1
exhibited a hole mobility of 0.11 cm V s . Other copolymers
in the series, poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyr-
rolo[3,4-c]pyrrole-1,4-dione-alt-phenylene} (PDPP-FPF) and
poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]
pyrrole-1,4-dione-alt-anthracene}
ꢀ1 ꢀ1
(PDPP-FAF)
2
and 0.07 cm V s , respectively. Bulk hetero-
showed
2
.04 cm V
ꢀ1 ꢀ1
0
s
junction OPV devices are fabricated by blending the donor
copolymer PDPP-FPF, PDPP-FNF or PDPP-FAF with [6,6]
phenyl-C71-butyric acid methyl ester ([70]PCBM) as the
acceptor. A power conversion efficiency of 2.6% is achieved using
the polymer PDPP-FNF with fullerene in a ratio of 1 : 2. The
Scheme 1 Synthesis of compound 4: (a) sodium, diisopropyl succinate,
ꢁ
iron chloride, tert-amyl alcohol, 110 C, 61%; (b) K
ꢁ
2
CO
3
, 2-octyl-1-
dodecyl bromide, anhydrous DMF, 120–130 C, 48%; (c) bromine,
chloroform, room temperature, 58%.
4
426 | J. Mater. Chem., 2012, 22, 4425–4435
This journal is ª The Royal Society of Chemistry 2012

View Online
3 4 2 3
Scheme 2 Synthesis of PDPP-FPF, PDPP-FNF, and PDPP-FAF: (a) Aliquat 336, Pd(PPh ) , 2 M K CO , toluene, reflux, 48 h.
ꢁ
Copolymerization was carried out at 80 C under argon atmo-
sphere for 72 h by reacting 3,6-bis(5-bromofuran-2-yl)-2,5-bis(2-
octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (4) with
Purified polymers PDPP-FPF, PDPP-FNF and PDPP-FAF
showed the number average molecular weights (M ) of 47 958 g
n
ꢀ1
ꢀ1
ꢀ1
mol , 53 609 g mol and 20 584 g mol with polydispersity
indices (PDI) of 2.65, 1.59 and 1.26 respectively as measured by
gel permeation chromatography (GPC) at a column temperature
1
,4-bis(4,4,5,5-tetramethyl-1,3,2-dioxabrolan-2-yl)phenylene (5)
in the presence of Pd(PPh ) as a catalyst, Aliquat 336 as a phase
3
4
ꢁ
transfer catalyst and 2 M K CO as a base in toluene via Suzuki
2
of 40 C with THF as an eluent and polymethylmethacrylate
3
coupling. A small amount of bromobenzene was added to the
reaction mixture and stirred for 5 h to eliminate the boronic ester
end group. Then a small amount of phenyl boronic acid was
added and stirred for additional 5 h to eliminate the bromo end
groups. The resulting reaction mixture was then poured into
a mixture of methanol and 2 M HCl and stirred for few hours
and the precipitate was filtered off and dried. The crude polymer
was then subjected to purification using Soxhlet extraction for
(PMMA) as standard (see GPC elution curves in the ESI†). The
lower molecular weight of PDPP-FAF is probably due to its poor
solubility in the reaction medium (toluene) arising from the
larger anthracene unit attached to the DBF moiety. The thermal
stability of the polymers was analyzed by thermogravimetric
analysis (TGA) under a nitrogen flow. PDPP-FPF, PDPP-FNF
ꢁ
ꢁ
and PDPP-FAF showed a 5% weight loss at 334 C, 350 C and
ꢁ
357 C, respectively, which indicates their excellent thermal
2
days using methanol, acetone, and hexane respectively for the
stability. GPC and thermal data are summarized in Table 1. DSC
ꢁ
removal of oligomers and catalytic impurities. The residue was
finally extracted with chloroform and precipitated again from
methanol, filtered, washed with methanol and dried to give
a dark solid of PDPP-FPF. Other two copolymers PDPP-FNF
and PDPP-FAF were synthesized and purified similarly using
characterization was carried out up to 330 C and only the
ꢁ
PDPP-FPF polymer exhibited an endothermic peak at 327 C
ꢁ
during heating scan and an exothermic peak at 310 C during the
subsequent cooling whereas for PDPP-FNF and PDPP-FAF no
2
,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxabrolan-2-yl)naphthalene (6)
Table 1 Polymerization results and thermal stability of the copolymers
and 2,8-bis(4,4,5,5-tetramethyl-1,3,2-dioxabrolan-2-yl)anthra-
cene (7) with the common comonomer 3,6-bis(5-bromofuran-
a
n
ꢀ1
b
w
ꢀ1
c
T
d
Polymers
M
/g mol
M
/g mol
PDI
2
-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (4) respectively. All three purified copolymers exhibited
good solubility in common organic solvents such as chloroform,
dichloromethane, THF, chlorobenzene and dichlorobenzene.
These polymers exhibit nice film forming properties and large
flakes of polymer films can be obtained after precipitating
polymers in a non-solvent such as methanol.
PDPP-FPF
PDPP-FNF
PDPP-FAF
47 958
53 609
20 584
127 425
85 760
25 987
2.65
1.59
1.26
334
350
357
a
b
Number-average molecular weight. Weight-average molecular weight
c
equivalent to PMMA interacting with the column. Decomposition
2
temperature (with 5% weight loss) determined by TGA under N .
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4425–4435 | 4427

View Online
37
systems. PDPP-FPF shows an absorption maximum (lmax) at
44 nm whereas other two polymers PDPP-FNF and PDPP-
7
FAF exhibit a maximum at 713 nm and 707 nm, respectively. It is
interesting to note that PDPP-FNF and PDPP-FAF show
shorter wavelengths compared to PDPP-FPF, despite naphtha-
lene and anthracene having longer conjugation length than
phenylene. The absorption peak position can be influenced by
the torsion angle between the DBF unit and acene moiety. A
large torsion angle could lead to localization of the p-electron
wave functions, and reduce conjugation along the polymer
38
backbone. Non-coplanar aromatic rings can be twisted out of
the plane due to steric hindrance which reduces the orbital
overlap and subsequently lowers the conjugation in polymer
chains. Such a kind of optical shift tuning has also been observed
1
in earlier DPP based polymer reports. Absorption maxima of
PDPP-FNF and PDPP-FAF are almost identical. Phenylene,
naphthalene and anthracene are weak electron donating six
membered rings in comparison to strong electron donating five
membered heterocyclic rings used in earlier reports of absorption
39
tuning. It is quite clear that optical properties of the donor–
acceptor copolymers severely depend on several parameters, i.e.,
strength of donors and acceptors, their attachment and planarity
in the backbone.
Solid state absorption measurements of these copolymers are
measured by spin coating their thin films on glass substrates,
shown in Fig. 1(b) (and Table 2). The absorption maxima in thin
films of PDPP-FPF, PDPP-FNF and PDPP-FAF are observed
at 749 nm, 715 nm and 713 nm respectively. As compared to the
Fig. 1 (a) Normalized UV-Vis-NIR absorption spectra in chloroform
and (b) thin film spectra of PDPP-FPF, PDPP-FNF and PDPP-FAF
copolymers.
thermal transition in the bulk sample was observed which may be
due to the more rigid backbone nature of the polymer.
2
.2 Optical properties
The UV-Vis absorption spectra of PDPP-FPF, PDPP-FNF and
PDPP-FAF as measured in chloroform solutions are shown in
Fig. 1a (and Table 2). All three copolymers possess wide
absorption from 300 nm to 800 nm. Shorter and longer wave-
length peaks are attributed to the p–p* transition band and
intramolecular charge transfer between donors and core DBF
moiety, respectively. Such multiple absorption bands are
a common feature of the donor–acceptor based conjugated
Fig. 2 (a) Photoelectron spectroscopy in air (PESA) measurements of
PDPP-FPF, PDPP-FNF and PDPP-FAF copolymer thin films spin
coated on glass/PEDOT:PSS substrates.
Table 2 Optical (UV-Vis and PL) and electrochemical properties of the copolymers
UV-Vis solution
l
UV-Vis thin film
Optical band
gap /eV
HOMO by
CV
Electrochemical
band gap /eV
a
b
c
d
e
f
g
Polymers
max /nm
lmax /nm
LUMO
HOMO by PESA
PDPP-FPF
PDPP-FNF
PDPP-FAF
671, 744
644, 713
640, 707
674, 749
645, 715
640, 713
1.55
1.63
1.64
5.40
5.34
5.33
3.88
3.85
3.80
5.48
5.50
5.52
1.52
1.49
1.53
a
b
Diluted solution in chloroform. Polymer film on a glass plate by spin coating from chloroform solution. Optical band gap calculated from the
c
d
absorption onset of the thin films. Measured from the oxidation onset of the CV. Calculated from the reduction onset. Obtained from the
e
f
g
photoelectron spectroscopy in air. Determined from the HOMO–LUMO difference.
4
428 | J. Mater. Chem., 2012, 22, 4425–4435
This journal is ª The Royal Society of Chemistry 2012

View Online
absorption spectrum observed in solution, the solid state
absorption spectra of the polymers have broader long wave-
length edges and a slight red shift in absorption maxima (2–
absorption spectrum are beneficial characteristics for light har-
vesting materials to be used in OPV devices.
6
nm). We also noticed such kind of observations related to small
2
.3 Electrochemical properties and photoelectron spectroscopy
shifts (solution vs. thin film) for other DPP furan based copoly-
9
mers. UV-Vis thin film spectra of PDPP-FPF, PDPP-FNF and
in air (PESA) measurements
PDPP-FAF copolymers are blue shifted compared to our earlier
9
The redox properties of organic semiconductors are commonly
used to estimate the energy levels of materials used in organic
electronic devices. The electrochemical behaviour of the PDPP-
FPF, PDPP-FNF and PDPP-FAF copolymers was characterized
by cyclic voltammetry (CV). Measurements were carried out at
reported furan based PDBFBT copolymer (lmax ¼ 770 nm)
where we used bithiophene as a comonomer block. This may be
due to the replacement of strong donor bithiophene by a weak
donor such as phenylene/naphthalene/anthracene and the extent
of donor–acceptor interactions involved in it. Optical band gaps,
calculated from absorption cut off values, are determined to be
ꢀ
1
room temperature using a scan rate of 50 mV s under nitrogen
in a 0.1 M tetrabutylammonium tetrafluoroborate (Bu NBF )
4
4
1
.55 eV, 1.63 eV and 1.64 eV for PDPP-FPF, PDPP-FNF and
solution in acetonitrile as the supporting electrolyte with ferro-
40,41
PDPP-FAF thin films respectively. Such low band gaps and wide
cene/ferrocenium ion as an internal standard.
A Pt electrode
Fig. 3 2-D XRD pattern intensity graphs and 2-D XRD images obtained with the incident X-ray perpendicular to the thin film stack of (a) PDPP-FPF,
b) PDPP-FNF and (c) PDPP-FAF copolymers.
(
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4425–4435 | 4429

View Online
Fig. 4 Output and transfer characteristics of PDPP-FPF (a), PDPP-FNF (b), and PDPP-FAF (c) copolymers. OTFT devices measured in a glove box
under nitrogen (L ¼ 100 mm; W ¼ 1 mm).
coated with the polymer film by drop casting was used as the
working electrode and Ag/AgCl was used as the reference elec-
trode. HOMO and LUMO values of the copolymers were
calculated from the oxidation and reduction onset potentials.
The electrochemical data for the three copolymers are summa-
rized in Table 2 and cyclic voltammograms are given in the ESI†.
The oxidation onsets for PDPP-FPF, PDPP-FNF and PDPP-
FAF copolymers were recorded at 1.00 V, 0.94 V and 0.93 V,
respectively. Using these values, the HOMO energy levels
calculated for PDPP-FPF, PDPP-FNF and PDPP-FAF are
5.40 eV, 5.34 eV and 5.33 eV respectively. PDPPF-FNF and
PDPP-FAF show comparable HOMO values. The LUMO
4
430 | J. Mater. Chem., 2012, 22, 4425–4435
This journal is ª The Royal Society of Chemistry 2012

View Online
Table 3 Summary of field effect mobilities (m), on/off ratios (Ion/Ioff) and
threshold voltages (V ) for the copolymers (top contact bottom gate
devices) prepared on OTS-treated substrates
processed thin film of PDPP-FPF, PDPP-FNF or PDPP-FAF
t
on octyltrichlorosilane (OTS) treated Si/SiO wafers. Gold was
2
thermally evaporated on top of the polymer film to form source/
drain electrode features, using a shadow mask. Current–voltage
2
ꢀ1 ꢀ1
Polymers
m
sat/cm V
s
V
t
/V
Ion/Ioff ratio
(
I–V) characteristics of OTFTs were measured under nitrogen. In
5
PDPP-FPF
PDPP-FNF
PDPP-FAF
0.04
0.11
0.07
ꢀ1.20
ꢀ40.6
ꢀ16.3
10
10
10
all cases OTFT devices showed characteristic p-channel field-
effect performance. The electrical properties of these OTFT
devices were evaluated, and output and transfer characteristics
are shown in Fig. 4. These curves depict good modulation in
source–drain current at various gate voltages and later on
current saturates at high gate voltages. The charge carrier
mobility is calculated from the saturation regime of the OTFT
transfer characteristics from the following equation.
5
5
energy levels calculated for PDPP-FPF, PDPP-FNF and PDPP-
FAF from their reduction onsets are 3.88 eV, 3.85 eV and
3
.80 eV, respectively. Additionally, we employed photoelectron
spectroscopy in air (PESA) to measure the ionization potential of
PDPP-FPF, PDPP-FNF and PDPP-FAF. The values obtained
from spin coated thin films of polymers on PEDOT:PSS coated
glass substrates are 5.48, 5.50 and 5.52 eV, respectively as shown
in Fig. 2. High ionization potentials are characteristic of oxida-
tive stable organic materials.
ꢀ
ꢀ
ꢀ
vIds
L
msat
¼
ꢀ
ꢀ
¼
À
Á
vVgs
WC V ꢀ V
d
V ¼const
i
g
o
2
.4 X-Ray diffraction (XRD) study
In order to study the solid state molecular packing and ordering
of the polymer, X-ray diffraction (XRD) measurements were
carried out on polymer flakes. Polymer flakes were prepared by
evaporating the solvent from a dilute polymer solution in chlo-
roform to form a thick polymer film in the flask, followed by
careful rinsing of the film with methanol (a non-solvent). The
polymer flakes (ꢂ100 mm thick) were then cut into small pieces
and used for 2-D XRD measurements. The 2-D-XRD diffraction
patterns and 2-D XRD images of the PDPP-FPF, PDPP-FNF
and PDPP-FAF copolymers are shown in Fig. 3; the incident
X-ray was perpendicular to the polymer flakes. All diffracto-
grams exhibit two peaks which correspond to interlayer
d-spacing and p–p stacking. The primary strong peak (100) at
ꢁ ꢁ ꢁ
4
.96 , 5.02 and 4.48 for PDPP-FPF, PDPP-FNF and PDPP-
ꢀ
ꢀ
FAF copolymers corresponds to a d-spacing of 17.79 A, 17.58 A
ꢀ
and 19.70 A, respectively. Small variations in interlayer d-spacing
values of PDPP-FPF, PDPP-FNF and PDPP-FAF most prob-
ably arise from the differences in conjugated backbone planarity
due to the torsion angle between DPP furan and comonomer
(
steric hindrance) as well as D–A intramolecular/intermolecular
interactions. The broad secondary diffraction peaks (010) for all
ꢁ
copolymers range from 2q ¼ 15 to 30 suggesting that these
copolymers are not highly crystalline. The diffraction peak
ꢁ
ꢁ
ꢁ
maxima (010) located at 2q ¼ 20.74 , 21.18 , and 20.08 for
PDPP-FPF, PDPP-FNF and PDPP-FAF can be assigned to the
ꢀ
face to face packing distances of 4.27 A, 4.18 A and 4.41 A
ꢀ
ꢀ
respectively. These values are similar to our earlier reported DPP
ꢀ
9
furan based PDBFBT copolymer (4.4 A). Such kind of broad
diffraction pattern and 2q value were also observed for other
42
DPP polymers such as C10-PPE-DPP. The distance estimated
ꢀ
from the broad peak, 4.2–4.4 A, reflects simply the short range
intermolecular distance due to van der Waals force, which
includes the p–p distance and the distance between other parts of
the polymer chains such as side chains.
2
.5 Organic thin film transistors (OTFTs)
Fig. 5 Current density–voltage curves of PDPP-FPF, PDPP-FNF and
PDPP-FAF copolymer devices, as blended with [70]PCBM in a 1 : 2
ratio.
Polymer OTFTs were fabricated using a bottom gate top contact
BGTC) device geometry having an ꢂ40 nm thick solution
(
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4425–4435 | 4431

View Online
Table 4 OPV performance of PDPP-FPF/[70]PCBM, PDPP-FNF/[70]PCBM, PDPP-FAF/[70]PCBM based devices with blend ratio 1 : 2 (w/w), active
layers were spin coated from chloroform of chloroform : DCB (4 : 1) (mix)
PDPP-FPF : [70]
PCBM (1 : 2)
chloroform
PDPP-FPF : [70]
PCBM
(1 : 2) mix
PDPP-FNF : [70]
PCBM (1 : 2)
chloroform
PDPP-FNF : [70]
PCBM
(1 : 2) mix
PDPP-FAF : [70]
PCBM (1 : 2)
chloroform
PDPP-FAF : [70]
PCBM
(1 : 2) mix
J
V
FF
SC
2.1
0.54
34
3.6
0.56
37
2.3
0.72
31
8.6
0.71
42
2.9
0.73
41
7.8
0.69
45
OC
PCE
Thickness/nm
0.39
65
0.78
80
0.51
80
2.6
70
0.84
60
2.5
70
where W and L are the channel width and length, respectively, Ci
(PCE z2.5%) than for the PDPP-FPF based device (PCE < 1%).
Mixed solvent systems or the incorporation of an additive into
the solution have been shown to influence the morphology of
is the capacitance per unit area of the dielectric layer. Linear
1
2
ds d gs
plots of the (I )/ vs. Vgs deduced from the I vs. V measure-
33,43–45
ments. The PDPP-FPF, PDPP-FNF and PDPP-FAF based
ꢀ1
blend films and the resultant performance of OPV devices.
2
ꢀ1
OTFT devices exhibit a hole mobility of 0.04 cm
ꢀ1 ꢀ1
V
s ,
Guidelines for solvent additives include selective solubility of the
2
.11 cm V
2
and 0.07 cm V s , respectively. PDPP-FNF
ꢀ1 ꢀ1
0
s
exhibits the highest hole mobility among the series of these
copolymers. PDPP-FNF may be more co-planar compared to
the other copolymers according to the dihedral angle between
DPP furan and naphthalene blocks (see ESI†) which promotes
stronger intramolecular interaction and better charge carrier
transport. These mobility values are significantly lower
9
compared to that of the previously reported PDBFBT; the
bithiophene donor block adjacent to the DBF block results in
stronger D–A intramolecular interactions than the acenes used
here. The OTFT device characteristics such as threshold voltage
(VTh) and on/off ratio are summarized in Table 3. Changing the
choice of acene block (from phenylene to anthracene) next to the
DBF block tunes the electrical properties of the PDPP-FPF,
PDPP-FNF and PDPP-FAF based OTFTs.
2
.6 Organic photovoltaic (OPV) devices
Organic photovoltaic devices were fabricated, utilizing each of
the three polymers as the donor material; the device structure was
ITO/PEDOT:PSS/PDPP-FXF : [70]PCBM(1 : 2)/Al, where ‘X’
represents either phenylene, naphthalene, or anthracene. The
active layer films were 60–80 nm thick, which were spun from
either chloroform or
a chloroform : ortho-dichlorobenzene
(
ODCB) (4 : 1 by volume) mixed solvent system. The J–V
characteristics are shown in Fig. 5 and the device performance is
summarized in Table 4. Devices made with films cast from
chloroform solutions show very modest performance; the short
ꢀ2
circuit current (J ) values are below 3 mA cm , the fill factors
sc
are below 41% and power conversion efficiencies are less than
1
%. The open circuit voltage (Voc) of the PDPP-FPF based
device is significantly lower than that for the PDPP-FNF and
PDPP-FAF based devices (0.54 V vs. 0.72 V and 0.73 V), despite
relatively similar ionization potentials as determined by PESA.
The origin of the reduced Voc is not clear; we speculate that poor
morphology, in the bulk or at the interface, may result in
recombination losses and lower the V . When ODCB was
oc
incorporated into the solvent system the J , FF, and PCE of the
sc
devices were improved, while the Voc remained relatively
constant. The fill factor improved slightly but was still low (<0.5)
suggesting a mismatch in carrier mobility and substantial loss of
carriers via recombination. The increase in performance was
more significant for PDPP-FNF and PDPP-FAF based devices
Fig. 6 (a) IPCE spectra of PDPP-FNF copolymer devices, as blended
with [70]PCBM in a 1 : 2 ratio from chloroform or chloroform : DCB
mix. (b). Normalized IPCE spectra of devices from chloroform or
chloroform : DCB mix. (c) Comparison of IPCE spectra of device and
optical absorption of the blend film.
4
432 | J. Mater. Chem., 2012, 22, 4425–4435
This journal is ª The Royal Society of Chemistry 2012

View Online
43
fullerene and a higher boiling point than the host solvent. As
a rough test of solubility of the polymers in ODCB the following
measurement was conducted. Polymer films were spin coated
from chloroform on glass/PEDOT:PSS substrates and the
optical absorptions of these films were measured with an Acton
spectrometer and an Ocean Optics calibrated light source (HL-
PDPP-FNF. Additionally, these polymer semiconductors are
also used as a donor with PC BM as an acceptor in OPV devices
7
1
and highest power conversion efficiencies (PCE) of 2.5 to 2.6%
were obtained for both PDPP-FNF and PDPP-FAF polymers
respectively.
4. Experimental
2
000-CAL). The samples were then ‘‘rinsed’’ with ODCB by
returning the substrate to the spin coater, covering the film with
ꢂ200 mL of ODCB and spinning for 1 min. The optical
absorption of the samples was then measured again, particular
attention was given to measuring the same spot as in the initial
measurement, and it should be noted that the film was smooth
and optically fairly uniform in both cases. The change in optical
density (DOD) of the films was ꢀ0.40, ꢀ0.06, and ꢀ0.21 for
PDPP-FPF, PDPP-FNF and PDPP-FAF, respectively. The
large change in PDPP-FPF absorption indicates that this poly-
mer has a better solubility in ODCB. Thus fullerene has little
selective solubility over PDPP-FPF in ODCB, which may
explain the small increase in device performance of PDPP-FPF:
PC71BM when employing the mixed solvent system as compared
with PDPP-FNF and PDPP-FAF.
4
.1 General
All the chemicals were purchased from Strem, Acros, and Sigma-
Aldrich and used without further purification. All reactions were
carried out using Schlenk techniques in an argon or nitrogen
atmosphere with anhydrous solvents. 1,4-Bis(4,4,5,5-tetra-
methyl-1,3,2-dioxabrolan-2-yl)phenylene (5) is available
commercially whereas 2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxab-
rolan-2-yl)naphthalene (6) and 2,8-bis(4,4,5,5-tetramethyl-1,3,2-
dioxabrolan-2-yl)anthracene (7) were synthesized in the
laboratory.
4
.2 Characterization
1 13
H and C NMR data were performed on a Bruker DPX
The IPCE spectra for PDPP-FNF devices from both chloro-
form and chloroform : ODCB solutions are shown in Fig. 6 (see
ESI† for other IPCE spectra). The device made from the mixed
solvent solution shows a much higher IPCE value throughout the
spectrum, in agreement with the larger Jsc. The resultant
morphology from the mixed solvent system is assumed to
provide a larger interfacial surface area between donor and
acceptor species and/or more complete percolation pathways for
charge transport. While the two spectra are similar in shape, the
mixed solvent system demonstrates a slightly higher relative
contribution in the longer wavelength region where the polymer
absorbs. It is interesting to note that the absorption spectrum of
the blend film is dominated by the absorption peaks of the
polymer in the longer wavelength region, and the absorption
spectrum is not strongly proportionate to the IPCE spectrum.
This may suggest that many excitons formed in the polymer are
not resulting in collected charge carriers, though the precise loss
mechanism is unclear at this time.
3
00 MHz or 400 MHz spectrometer with chemical shifts refer-
enced to residual CHCl and H O in CDCl . Matrix assisted
3
2
3
laser desorption/ionization time-of-flight (MALDI-TOF) mass
spectra were obtained on a Bruker Autoflex TOF/TOF instru-
ment using dithranol as a matrix. Gel permeation chromatog-
raphy (GPC) analysis against polymethylmethacrylate (PMMA)
ꢁ
standards was performed in THF at 40 C on a Waters high
pressure GPC assembly with an M590 pump (model 2690), m-
ꢀ
Styragel columns of 105, 104, 103, 500 and 100 A and a refractive
index (RI) detector. A typical concentration, 1.5 mg weight of
polymer dissolved in 1 mL of THF, was used for running GPC
samples. UV-Vis spectra were recorded on a Shimadzu model
2
501-PC. Photoluminescence (PL) spectra were measured on
a Perkin-Elmer (LS50B) spectrofluorimeter. Cyclic voltammetry
experiments were performed using an Autolab potentiostat
(
model PGSTAT30) by Echochimie. All CV measurements were
recorded in solid state with 0.1 M tetrabutylammonium hexa-
fluorophosphate as the supporting electrolyte (scan rate of
ꢀ1
1
00 mV s ). The experiments were performed at room temper-
3
. Conclusion
ature with a conventional three-electrode configuration consis-
ting of a platinum disc working electrode, a gold counter
electrode, and an Ag/AgCl reference electrode using ferrocene/
ferrocinium ion as an internal standard. The working platinum
electrode was coated with the polymer thin film by using
a polymer solution in chloroform. The HOMO energy level was
A series of donor–acceptor copolymers containing DPP furan
with phenylene, naphthalene and anthracene have been designed
and synthesized via palladium-catalyzed Suzuki poly-
condensation in good yields. Poly{3,6-difuran-2-yl-2,5-di(2-
octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-phenylene}
calculated using the equation EHOMO ¼ E
+ 4.4 eV, where
ox-onset
(
PDPP-FPF), poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyr-
Eox-onset is the onset potential for oxidation relative to the Ag/
46–48
rolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene} (PDPP-FNF) and
poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]
pyrrole-1,4-dione-alt-anthracene} (PDPP-FAF) exhibit higher
molecular weights with excellent thin film forming properties.
Optical and electrochemical band gaps were measured in the
range of 1.55–1.64 eV, indicating that they are potential light
harvesting materials for organic photovoltaics. These polymers
exhibit excellent p-channel charge transport characteristics when
used as the active semiconductor layer in organic thin-film
AgCl reference electrode.
Differential scanning calorimetry
(
DSC) was carried out under nitrogen on a TA Instruments DSC
ꢀ1
ꢁ
Q100 instrument (scanning rate of 10 C min ). Thermogravi-
metric analysis (TGA) was carried out using a TA Instruments
ꢁ
ꢀ1
TGA Q500 instrument (heating rate of 10 C min ).
4
.3 Synthesis of poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-
pyrrolo[3,4-c]pyrrole-1,4-dione-alt-phenylene} (PDPP-FPF)
2
transistor (OTFT) devices. The highest hole mobility of 0.11 cm
ꢀ1
To a 50 mL Schlenk flask, 3,6-bis(5-bromofuran-2-yl)-2,5-bis-
ꢀ1
V
s
is achieved in bottom gate/top-contact OTFT devices for
(2-octyl-1-dodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (4)
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4425–4435 | 4433

View Online
(
0.350 g, 0.34 mmol) and 1,4-bis(4,4,5,5-tetramethyl-1,3,2-diox-
off and subjected to Soxhlet extraction for 2 d in methanol,
acetone, and hexane for the removal of oligomers and catalytic
impurities. The remaining polymer was extracted with chloro-
form and precipitated again from methanol, filtered, washed with
methanol, and dried under vacuum at room temperature
abrolan-2-yl)phenylene (5) (0.112 g, 0.34 mmol), 2 M aqueous
K CO solution (5 mL) and 2 drops of Aliquat 336 were dis-
2
3
solved in toluene (10 mL). The solution was purged with argon
for 30 min, and then tetrakis(triphenylphosphine)palladium
ꢁ
(
15 mg, 0.012 mmol) was added. The reaction was stirred at 80 C
(0.190 g, 47% yield). M
w
/M
n
(GPC) ¼ 20 584/25 987. UV-Vis:
for 3 d. Then a toluene solution of phenyl boronic acid was added
and the mixture was stirred for additional 4 h, followed by
addition of a few drops of bromobenzene and stirred overnight.
The resulting mixture was poured into a mixture of methanol and
water and stirred for few hours. The resulting solid was filtered
off and subjected to Soxhlet extraction for 2 d in methanol,
acetone, and hexane for the removal of oligomers and catalytic
impurities. The remaining polymer was extracted with chloro-
form and precipitated again from methanol, filtered, washed with
methanol, and dried under vacuum at room temperature
640, 707 nm (in chloroform); 640, 713 nm (thin film).
4
.6 OTFT fabrication and characterization
Top contact/bottom gate OTFT devices were fabricated using
+
p -Si/SiO substrates where p -Si and SiO work as gate elec-
+
2
2
trode and gate dielectric, respectively. The thickness of thermally
grown silicon oxide layer is around ꢂ200 nm with a capacitance
ꢀ2
of about 15 nF cm . Substrates were cleaned using ultra-
sonication in acetone, methanol and de-ionized water. The
cleaned substrates were dried under a nitrogen flow and heated at
(
0.290 g, 94% yield). M
w
/M
n
(GPC) ¼ 47 958/127 425. UV-Vis:
ꢁ
6
71, 744 nm (in chloroform); 674, 749 nm (thin film).
100 C for 5 min. The substrates were then treated in UV-ozone
for 20 min. Then, the substrates were kept in a desiccator with
a few drops of octyltrichlorosilane (OTS). The desiccator was
4
.4 Synthesis of poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-
ꢁ
evacuated for 3 min and placed in an oven at 110 C for 3 h. The
pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene} (PDPP-FNF)
substrates were removed from the desiccator, thoroughly rinsed
with isopropanol, and dried under a nitrogen flow. PDPP-FPF,
PDPP-FNF and PDPP-FAF polymeric thin films were deposited
To a 50 mL Schlenk flask, 3,6-bis(5-bromofuran-2-yl)-2,5-bis(2-
octyl-1-dodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
(4)
ꢀ1
(
0.350 g, 0.35 mmol) and 2,6-bis(4,4,5,5-tetramethyl-1,3,2-diox-
via spin coating using 8 mg mL solution in chloroform on the
OTS treated Si/SiO2 substrates. Subsequently, on top of the
polymer active layer, a roughly 100 nm thick gold (Au) thin film
was deposited for source (S) and drain (D) electrodes through
a shadow mask. For a typical OTFT device reported here, the
source–drain channel length (L) and channel width (W) were
100 mm and 1 mm, respectively. The device characteristics of the
OTFTs were measured at room temperature under nitrogen with
a Keithley 4200 source meter. The field effect mobility (m) was
calculated from the saturation regime of transfer characteristics.
abrolan-2-yl)naphthalene (6) (0.135 g 0.35 mmol), 2 M aqueous
K CO solution (5 mL) and 2 drops of Aliquat 336 were dis-
2
3
solved in toluene (10 mL). The solution was purged with argon
for 30 min, and then tetrakis(triphenylphosphine)palladium
ꢁ
(
15 mg, 0.012 mmol) was added. The reaction was stirred at 80 C
for 3 d. Then a toluene solution of phenyl boronic acid was added
and the mixture was stirred for additional 4 h, followed by
addition of a few drops of bromobenzene and stirred overnight.
The resulting mixture was poured into a mixture of methanol and
water and stirred for few hours. The resulting solid was filtered
off and subjected to Soxhlet extraction for 2 d in methanol,
acetone, and hexane for the removal of oligomers and catalytic
impurities. The remaining polymer was extracted with chloro-
form and precipitated again from methanol, filtered, washed with
methanol, and dried under vacuum at room temperature
4
.7 OPV fabrication and its characterization
For solar cell device fabrication, patterned indium tin oxide
(ITO)-coated glass substrates were purchased from Kintec Co.
The glass/ITO substrates were cleaned by ultrasonication in
subsequent baths of detergent (15 min), de-ionized water
(
0.300 g, 69% yield). M
w
/M
n
(GPC) ¼ 53 609/85 760. UV-Vis:
6
44, 713 nm (in chloroform); 645, 715 nm (thin film).
(15 min), acetone (15 min), methanol (15 min) and isopropanol
ꢁ
(
15 min). The substrates were then dried at 80 C for several
hours in an oven. The substrates were UV-ozone cleaned for 10
minutes prior to the spin coating of a 40 nm thick PEDOT:PSS
hole transporting layer (Clevios P VP AI 4083). The active layer
of PDPP-FPF : [70]PCBM, PDPP-FNF : [70]PCBM and
PDPP-FAF : [70]PCBM using 1 : 2 ratios was spin coated on
PEDOT:PSS deposited ITO glass. An aluminium cathode was
deposited by thermal evaporation through a shadow mask under
4
.5 Synthesis of poly{3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-
pyrrolo[3,4-c]pyrrole-1,4-dione-alt-anthracene} (PDPP-FAF)
To a 50 mL Schlenk flask, 3,6-bis(5-bromofuran-2-yl)-2,5-bis(2-
octyl-1-dodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
0.400 g, 0.40 mmol) and 2,8-bis(4,4,5,5-tetramethyl-1,3,2-diox-
abrolan-2-yl)anthracene (7) (172 g, 0.40 mmol), 2 M aqueous
CO solution (6 mL) and 2 drops of Aliquat 336 were dis-
(4)
(
ꢀ5
K
2
3
a pressure of roughly 10 mbar to complete the devices, having
2
a device area of 9 mm . The IPCE (Incident Photon-to-current
solved in toluene (12 mL). The solution was purged with argon
for 30 min, and then tetrakis(triphenylphosphine)palladium
ꢁ
Conversion Efficiency) was measured with a testing system
consisting of an Oriel 300 W Xe lamp in combination with
a monochromator (Oriel Cornerstone 130), and lock-in amplifier
(Stanford Research Systems, SRS 810); the incident light inten-
sity was determined by a calibrated Si photodiode. The current–
voltage characteristics were measured using a source meter
(Keithley 2400), while irradiance was provided by a solar
(
20 mg, 0.017 mmol) was added. The reaction was stirred at 80 C
for 3 d. Then a toluene solution of phenyl boronic acid was added
and the mixture was stirred for additional 4 h, followed by
addition of a few drops of bromobenzene and stirred overnight.
The resulting mixture was poured into a mixture of methanol and
water and stirred for few hours. The resulting solid was filtered
4
434 | J. Mater. Chem., 2012, 22, 4425–4435
This journal is ª The Royal Society of Chemistry 2012

View Online
simulator (Steuernagel, Germany model 535). The simulator
lamp intensity was set using a reference cell (Hamamatsu S1787-
19 A. P. Zoombelt, S. G. J. Mathijssen, M. G. R. Turbiez, M. M. Wienk
and R. A. J. Janssen, J. Mater. Chem., 2010, 20, 2240.
2
0 J. C. Bijleveld, V. S. Gevaerts, D. D. Nuzzo, M. Turbiez,
S. G. J. Mathijssen, D. M. de Leeuw, M. M. Wienk and
R. A. J. Janssen, Adv. Mater., 2010, 22, E242.
0
4) and the calculated spectral mismatch factor.
2
2
2
1 J. C. Bijleveld, R. A. M. Verstrijden, M. M. Wienk and
R. A. J. Janssen, J. Mater. Chem., 2011, 21, 9424.
2 C. Kanimozhi, P. Balraju, G. D. Sharma and S. Patil, J. Phys. Chem.
B, 2010, 114, 3095.
Acknowledgements
The authors acknowledge the Visiting Investigatorship Pro-
gramme (VIP) of the Agency for Science, Technology and
Research (A*STAR), Republic of Singapore for financial
support. We are also thankful to Mr Lim Poh Chong and Ting
Ting Lin for 2-D XRD measurement and theoretical modelling
respectively.
3 J. Roncali, Chem. Rev., 1992, 92, 711.
24 T. Yamamoto, Macromol. Rapid Commun., 2002, 23, 583.
25 J. Chen and Y. Cao, Acc. Chem. Res., 2009, 42, 1709.
2
6 D. Reitzenstein, PhD dissertation, Julius-Maximillians University,
Wurzberg, 2010.
2
2
7 Y. Zu, PhD dissertation, Koln University, Koln, 2006.
8 L. I. Bellenkii and V. N. Gramenitskaya, The literature of heterocyclic
chemistry, part-VIII, Adv. Heterocycl. Chem., 1999–2001, 87, p. 1
References
(
2004).
1
B. Tieke, A. R. Rabindranath, K. Zhang and Y. Zhu, Beilstein J. Org.
Chem., 2010, 6, 830.
29 S. Andoa, A. Nishida, E. Fujiwara, H. Tadab, Y. Inoue, S. Tokito
and Y. Yamashita, Synth. Met., 2006, 156, 327.
2
L. B u€ rgi, M. Turbiez, R. Pfeiffer, F. Bienewald, H. Kirner and
C. Winnewisser, Adv. Mater., 2008, 20, 2217.
Y. Li, US Pat., 2009/65766 A1 and 2009/0065878A1, 2009.
J. C. Bijleveld, A. P. Zoombelt, S. G. J. Mathijssen, M. M. Wienk,
M. Turbiez, D. M. de Leeuw and R. A. J. Janssen, J. Am. Chem.
Soc., 2009, 131, 16616.
Y. Li, S. P. Singh and P. Sonar, Adv. Mater., 2010, 22, 4862.
P. Sonar, S. P. Singh, Y. Li, M. S. Soh and A. Dodabalapur, Adv.
Mater., 2010, 22, 5409.
Y. Li, P. Sonar, S. P. Singh, M. S. Soh, M. van Meurs and J. Tan, J.
Am. Chem. Soc., 2011, 133, 2198.
30 T. Minari, Y. Miyata, M. Terayama, T. Nemoto, T. Nishinaga,
K. Komatsu and S. Isoda, Appl. Phys. Lett., 2006, 88, 083514.
31 T.-L. Choi, K.-M. Han, J.-I. Park, D.-H. Kim, J.-M. Park and S. Lee,
Macromolecules, 2010, 43, 6045.
32 C. H. Woo, P. M. Beaujuge, T. W. Holcombe, O. P. Lee and
J. M. J. Fr ꢁe chet, J. Am. Chem. Soc., 2010, 132, 15547.
33 J. C. Bijleveld, B. P. Karsten, S. G. J. Mathijssen, M. M. Wienk,
D. M. de Leeuw and R. A. J. Janssen, J. Mater. Chem., 2011, 21, 1600.
34 O. Gidron, A. Dadvand, Y. Sheynin, M. Bendikov and
D. F. Perepichka, Chem. Commun., 2011, 47, 1976.
35 J. T. Lin, P. C. Chen, Y. S. Yen, Y. C. Hsu, H. H. Chou and
M. C. P. Yeh, Org. Lett., 2009, 11, 97.
36 B. Walker, A. B. Tomayo, X. D. Dang, P. Zalar, J. H. Seo, A. Garcia,
M. Tantiwiwat and T. Q. Nguyen, Adv. Funct. Mater., 2009, 19, 3063.
37 J. Roncali, Chem. Rev., 1997, 97, 173.
3
4
5
6
7
8
9
P. Sonar, S. P. Singh, Y. Li, Z.-E. Ooi, T.-J. Ha, I. Wong, M. S. Soh
and A. Dodabalapur, Energy Environ. Sci., 2011, 22, 5409.
Y. Li, P. Sonar, S. P. Singh, W. Zeng and M. S. Soh, J. Mater. Chem.,
2011, 21, 10829.
1
0 H. Bronstein, Z. Y. Chen, R. S. Ashraf, W. M. Zhang, J. P. Du,
J. R. Durrant, P. S. Tuladhar, K. Song, S. E. Watkins, Y. Geerts,
M. M. Wienk, R. A. J. Janssen, T. Anthopoulos, H. Sirringhaus,
M. Heeney and I. McCulloch, J. Am. Chem. Soc., 2011, 133, 3272.
1 J. S. Ha, K. H. Kim and D. H. Choi, J. Am. Chem. Soc., 2011, 133, 10364.
2 T. L. Nelson, T. M. Young, J. Y. Liu, S. P. Mishra, J. A. Belot,
C. L. Balliet, A. E. Javier, T. Kowalewski and R. D. McCullough,
Adv. Mater., 2010, 22, 4617.
38 H. A. M. van Mullekom, J. Vekemans, E. E. Havinga and
E. W. Meijer, Mater. Sci. Eng., R, 2001, 32, 1.
39 H. Zhou, L. Yang, S. Stoneking and W. You, ACS Appl. Mater.
Interfaces, 2010, 2, 1377.
40 G. Gritzner and J. Kuta, Pure Appl. Chem., 1984, 56, 461.
41 G. Gritzner, Pure Appl. Chem., 1990, 62, 1839.
42 G. Zhang, K. Liu, Y. Li and M. Yang, Polym. Int., 2009, 58, 665.
43 J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D. Moses, A. J. Heeger
and G. C. Bazan, Nat. Mater., 2007, 6, 497.
44 J. K. Lee, L. W. Ma, C. J. Brabec, J. Yuen, J. S. Moon, J. Y. Kim,
K. Lee, G. C. Bazan and A. J. Heeger, J. Am. Chem. Soc., 2008,
130, 3619.
45 C. H. Woo, P. M. Beaujuge, T. W. Holcombe, O. P. Lee and
J. M. J. Frechet, J. Am. Chem. Soc., 2010, 132, 15547.
46 Y. Li, J. Ding, M. Day, Y. Tao, J. Lu and M. D’iorio, Chem. Mater.,
2004, 16, 2165.
47 D. M. Leeuw, M. M. J. Simenon, A. R. Brown and
R. E. F. Einerhand, Synth. Met., 1997, 87, 53.
48 Y. Cui, X. Zhang and S. A. Jenekhe, Macromolecules, 1999, 32, 3824.
1
1
1
1
3 J. Lee, S. Cho and C. Yang, J. Mater. Chem., 2011, 21, 8528.
4 T.-J. Ha, P. Sonar and A. Dodabalapur, Appl. Phys. Lett., 2011, 98,
2
53305.
5 M. M. Wienk, M. Turbiez, J. Gilot and R. A. J. Janssen, Adv. Mater.,
008, 20, 2256.
1
1
1
1
2
6 E. Zhou, S. Yamakawa, K. Tajima, C. Yang and K. Hashimoto,
Chem. Mater., 2009, 21, 4055.
7 Y. Zou, D. Gendron, R. Neagu-Plesu and M. Leclerc,
Macromolecules, 2009, 42, 6361.
8 L. Huo, J. Hou, H. Chen, S. Zhang, Y. Jiang, T. L. Chen and
Y. Yang, Macromolecules, 2009, 42, 6564.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4425–4435 | 4435