A timely synthetic tailoring of biaxially extended thienylenevinylene-like polymers for systematic investigation on field-effect transistors

Article abstract of DOI:10.1002/adfm.201403527

Considering there is growing interest in the superior charge transport in the ( E )-2-(2-(thiophen-2-yl)-vinyl)thiophene (TVT)-based polymer family, an essential step forward is to provide a deep and comprehensive understanding of the structure-property relationships with their polymer analogs. Herein, a carefully chosen set of DPP-TVT-n polymers are reported here, involving TVT and diketopyrrolopyrrole (DPP) units that are constructed in combination with varying thiophene content in the repeat units, where n is the number of thiophene spacer units. Their OFET characteristics demonstrate ambipolar behavior; in particular, with DPP-TVT-0 a nearly balanced hole and electron transport are observed. Interestingly, the majority of the charge-transport properties changed from ambipolar to p-type dominant, together with the enhanced hole mobilities, as the electron-donating thiophene spacers are introduced. Although both the lamellar d-spacings and π-stacking distances of DPP-TVT-n decreased with as the number of thiophene spacers increased, DPP-TVT-1 clearly shows the highest hole mobility (up to 2.96 cm² V^-11 s^-1) owing to the unique structural conformations derived from its smaller paracrystalline distortion parameter and narrower plane distribution relative to the others. These in-depth studies should uncover the underlying structure-property relationships in a relevant class of TVT-like semiconductors, shedding light on the future design of top-performing semiconducting polymers.

Full text of DOI:10.1002/adfm.201403527

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A Timely Synthetic Tailoring of Biaxially Extended
Thienylenevinylene-Like Polymers for Systematic
Investigation on Field-Effect Transistors
Dohyuk Yoo, Benjamin Nketia-Yawson, Seok-Ju Kang, Hyungju Ahn, Tae Joo Shin,
Yong-Young Noh,* and Changduk Yang*
(OFETs) with solution-processable semi-
Considering there is growing interest in the superior charge transport in
the (E)-2-(2-(thiophen-2-yl)-vinyl)thiophene (TVT)-based polymer family, an
essential step forward is to provide a deep and comprehensive understanding
of the structure–property relationships with their polymer analogs. Herein, a
carefully chosen set of DPP-TVT-n polymers are reported here, involving TVT
and diketopyrrolopyrrole (DPP) units that are constructed in combination
with varying thiophene content in the repeat units, where n is the number of
thiophene spacer units. Their OFET characteristics demonstrate ambipolar
behavior; in particular, with DPP-TVT-0 a nearly balanced hole and electron
transport are observed. Interestingly, the majority of the charge-transport
properties changed from ambipolar to p-type dominant, together with the
enhanced hole mobilities, as the electron-donating thiophene spacers are
introduced. Although both the lamellar d-spacings and π-stacking distances
of DPP-TVT-n decreased with as the number of thiophene spacers increased,
DPP-TVT-1 clearly shows the highest hole mobility (up to 2.96 cm2 V−1 s−1)
owing to the unique structural conformations derived from its smaller parac-
rystalline distortion parameter and narrower plane distribution relative to the
others. These in-depth studies should uncover the underlying structure–prop-
erty relationships in a relevant class of TVT-like semiconductors, shedding
light on the future design of top-performing semiconducting polymers.
conducting polymers as
a result of
combined efforts in developing novel
materials, optimizing microstructures
of semiconducting film, achieving two-
dimensional long-range order, and under-
standing charge transport physics.[1] In
order to achieve high mobilities with these
polymer semiconductors, new design
motifs have been introduced in recent
years in the form of the frameworks of
maximizing intra- and inter-molecular
charge transport by high co-planarity,
favorable orientation of polymer chain,
and strong intermolecular interactions
between the neighboring molecules.[2] In
line with this consideration, diketopyrro-
lopyrrole (DPP) has been suggested as a
promising building block for constructing
high-performance semiconducting poly-
mers owing to its tight π–π spacing and
long-range order induced by the high
co-planarity and cross-axis dipole.[1k,3]
Another appealing strategy to promote a
structurally strong inter-chain aggregates
is to utilize alternating electron-donating
(D) and electron-accepting (A) blocks in
the polymer backbones, utilizing the attractive forces between
the D and A units in the neighborhood molecules.
1. Introduction
Recently, impressive progress has been made in the field of
the charge carrier mobilities of organic field-effect transistors
Consequently, a current central design principle for devel-
oping top-performing semiconducting polymers in OFETs is
utilizing a class of D–A polymers based on DPP. In the last
5 years, the number of publications concerning DPP-based
polymers has increased 30-fold and is expected to rise further,
shedding light on the outstanding charge-transport efficacy.[4]
Alongside the above examples, a notable molecular set-up has
recently been described by Liu et al., (E)-2-(2-(thiophen-2-yl)-
vinyl)thiophene (TVT)-containing DPP polymers (previously
called PDVTs), which has been verified as producing one of
the highest mobilities observed to date for polymer semicon-
ductors. In this method, incorporating a vinylene linkage adja-
cent to two thiophene rings led to an increase in the degree
of co-planarity and π-conjugation along the polymer back-
bone through the reduced steric hindrance, thereby effectively
enhancing charge transport. Following on from this, a variety
of TVT-based structural derivatives, such as a naphthalenedi-
imide (NDI)-based polymer with TVT units and selenienylene
D. H. Yoo, Prof. C. Yang
Department of Energy Engineering
School of Energy and Chemical Engineering
Low Dimensional Carbon Materials Center
Ulsan National Institute of Science and Technology (UNIST)
Ulsan 689–798, South Korea
E-mail: yang@unist.ac.kr
B. Nketia-Yawson, Dr. S.-J. Kang, Prof. Y.-Y. Noh
Department of Energy and Materials Engineering
Dongguk University
26 Pil-dong, 3 ga, Jung-gu, Seoul 100–715, South Korea
E-mail: yynoh@dongguk.edu
Dr. H. Ahn, Dr. T. J. Shin
Pohang Accelerator Laboratory
Pohang University of Science and Technology
Pohang, Kyungbuk 790–784, South Korea
DOI: 10.1002/adfm.201403527
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DOI: 10.1002/adfm.201403527
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vinylene analogues of PDVTs have been developed successfully
with reasonably high mobility.[5] This indicates that TVT is
one of the most promising blocks for outperforming semicon-
ducting polymers; however, it has not been investigated system-
atically for the biaxially extended TVT-like polymers so far.
Therefore, with the aim of widening the understanding of
TVT-like polymers, the goals in this work focus on to the effects
on the intrinsic properties—including energetics, morphology,
molecular packing, and charge transport—of altering the thio-
phene to vinylene ratio in the DPP-TVT-based polymer family.
In order to achieve this goal, three DPP-TVT-n polymers, where
n is the number of thiophene spacer units between DPP and
TVT blocks in the repeat unit, were synthesized and character-
ized, and the results were discussed in terms of establishing
structure–property correlations. Notably, it was discovered that
structural stacking-type conformations of polymers, such as
degrees of paracrystalline and (h00) plane distribution, rather
than densely packed organization, play a dramatic role in facili-
tating charge transport.
transition, while the low-energy broad band (530–1100 nm)
is assigned to excited states with a prevalent highest occu-
pied molecular orbital (HOMO)–lowest unoccupied molecular
orbital (LUMO) contribution, and is classified as intra-molecular
charge transfer states (ICT). Passing from solution to thin film,
there is only slight difference in the absorption maxima of all
polymers, whereas together with light broadening in the peaks,
a red shift in their onsets is observed in the range of 26−63 nm.
This implies that the aggregation or orderly π−π stacking occurs
in the solid state, which is helpful for improving the charge-
transport in the film.[7] In addition, in comparison with the
absorption spectra in solution, a closer viewing of the spectra
revealed that 0–0 vibrational transition decreased, whereas 0–1
increased in both DPP-TVT-1 and DPP-TVT-2 films. It was con-
sidered very interesting that the ICT transitions of the polymers
were not only blue-shifted, but enhanced intensity of the ICT
peaks relative to the corresponding π−π* transition ones was
observed as a function of the increased numbers of thiophene
rings. It is evident that the strength of ICT complexes between
DPP and TVT units is quite sensitive to the concentration of
thiophene spacers. Consequently, the optical bandgaps from
the onset absorption of the polymer films follows the order:
DPP-TVT-2 > DPP-TVT-1 > DPP-TVT-0, which is an opposite
trend in comparison with the magnitude of the π-extension of
the donor conjugation, which increases alongside the number
of thiophene rings in the repeating unit. Similar phenomena
were observed for other bis-lactam-based polymers.[8] Further
experiments are currently underway to gain an understanding
of the unexpected chromatic shift.
Cyclic voltammetry (CV) was used to investigate the molec-
ular energy levels (HOMO and LUMO) of the three polymers,
exhibiting two reversible reductions and a strong quasi-revers-
ible oxidation for all the polymers (see Figure 1c and Table 1).
It might be expected that by changing the number of electron-
donating thiophene spacers, the HOMOs would be selectively
affected, with the LUMOs being almost unchanged.[9] How-
ever, the change in the thiophene content in DPP-TVT-n was
found to have as significant an influence on the LUMO levels
of the polymers as on the HOMO levels; in fact, its effects on
the LUMO levels were more pronounced (ranging from −3.55
to −3.23 eV). The LUMOs increased significantly with the
number of thiophene spacers, resulting in an increase in the
electrochemical bandgaps. This trend coincides closely with
the optical bandgaps described above. Ultraviolet photoelectron
spectroscopy (UPS) was also used to measure the ionization
potential (IP) levels of all the polymers (see Figure 1d). Similar
variation trends were found, further confirming the CV results.
Through B3LYP/6–31G calculation on the trimer length oli-
gomers, the theoretical molecular orbital distributions of the
optimized structures for the polymer series were visualized; this
is illustrated collectively in Figure 1e. In addition to the high co-
planarity for all cases, the electron densities of the HOMO and
LUMO for DPP-TVT-0-based model are both well delocalized
over the conjugated repeat unit, whereas the trimeric systems
for DPP-TVT-1 and DPP-TVT-2 demonstrated a similar den-
sity of states distribution for both the HOMO and LUMO wave
functions. The HOMO levels were well spread across the whole
of the molecules with the LUMOs being mostly localized on the
DPP acceptors.
2. Results and Discussion
2.1. Synthesis and Characterization
Based on published procedures, dithienyl-substituted DPP 1
was obtained by through the reaction of 2-thienylnitrile with
diisopropyl succinate, followed by the installation of side-
chins via alkylation.[6] Bromination of 1 using either one or
two equivalents of N-bromosuccinimide (NBS) led to the gen-
eration of compounds 2 and 3, which were subsequently sub-
jected to Stille coupling with either 2-trimethylstannylthiophene
or 5-trimethylstannyl-2,2′-bithiophene to produce the corre-
sponding DPP skeletons (4 and 5) with dissymmetric changes in
the appended neighboring thiophene content. Both units were
readily converted into dibrominated monomers 6 and 7 under
treatment with NBS, respectively (Scheme 1a). The dibromi-
nated monomers 3, 6, or 7 were copolymerized with trans-1,2-
bis(tributylstannyl)ethylene via Stille-coupling polymerization to
yield the target DPP-TVT-n polymers, respectively. The polymers
are depicted in Scheme 1b. All polymers were purified using
multiple Soxhlet extraction followed by dissolution-precipitation.
The average molecular weights (Mn) of the three polymers were
in the range 23.5−49.2 kDa with polydispersity indices (PDI) of
1.9−2.9, as determined using gel permeation chromatography
with THF as the eluent (Table 1). All polymers were found to
have satisfactory Mn values; the rather moderate Mn found for
DPP-TVT-2 can be attributed to its reduced solubility resulting
from the increased thiophene content in the backbone.
2.2. Optical and Electrochemical Properties as well as
Theoretical Calculations
Figure 1 is a plot of the optical absorption spectra of DPP-
TVT-0, DPP-TVT-1, and DPP-TVT-2 in solution (a) and in the
solid state (b). Each polymer presents two absorption bands;
the high-energy band (350–470 nm) is assigned to excited states
more localized on the thiophene units and defined as the π–π*
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DOI: 10.1002/adfm.201403527

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-
-
- -
DPP TVT 2
-
-
DPP TVT 1
DPP TVT 0
Polymer
Condition
Monomer (Yield %)
3 (67%)
6 (61%)
DPP-TVT-0
trans-1,2-bis(tributylstannyl)ethylene,
Pd2(dba)3, P(o-tolyl)3, toluene, 120 °C
DPP-TVT-1
DPP-TVT-2
7 (56%)
Scheme 1. a) Synthetic routes of monomers and b) chemical structures of DPP-TVT-n.
2.3. Electrical Characterization and Performance of OFETs
deposited to create a gate-dielectric layer, and the devices were
then baked at 80 °C for 1 h. All devices had a channel width
(W) of 1000 µm and a channel length (L) of 10–50 µm, respec-
tively. Details of the fabrication of the devices are included in
the Experimental section. The output and transfer curves data
for all devices are illustrated in Figure 3, and S1–3, and the
extracted electrical parameters of the OFETs are listed in Table 2,
and S1. Upon annealing at a temperature of 200 °C, the elec-
trical performance of all the devices was improved significantly,
demonstrating the highest value in average hole mobilities
(µh,avg) from DPP-TVT-n OFETs, as indicated in Figure 2. In
particular, DPP-TVT-0 was significantly affected by the temper-
ature during the annealing process. However, in the cases of
Top-gate/bottom-contact (TG/BC) OFETs were fabricated
using DPP-TVT-n polymers as the active layer. The TG/BC
OFETs were fabricated on glass substrates without any sur-
face treatment. The semiconducting layers were deposited
on the pre-patterned Ni/Au (t ≈ 3 nm/t ≈ 13 nm) source and
drain electrodes by spin coating of the polymer solutions (5 mg
mL−1) in 1,2,4-trichlorobenzene (TCB) at 1000 rpm for 30 s in a
nitrogen-filled glove box (oxygen and moisture <10 ppm). The
devices were then annealed at temperatures ranging between
150 and 250 °C on a hot plate for 30 min in the same glove box.
Subsequently, ≈500 nm-thick PMMA (Ci = 6.20 nF cm−2) was
Table 1. Molecular weights, and optical and electrochemical properties of the DPP-TVT-n polymers.
Polymer
Mn
[kDa]/PDI
EHOMO
[eV]b)
ELUMO
[eV]b)
λ
Egopt
[eV]a)
solution
max
[nm]
thinfilm
max
[nm]
UPS
[eV]c)
λ
E
IP
DPP-TVT-0
DPP-TVT-1
DPP-TVT-2
48.4/2.0
49.2/1.9
23.5/2.9
4.94
4.83
4.80
811, 887
760, 808
723
819, 903
758, 812
720
1.22
1.34
1.37
−5.28
−5.18
−5.13
−3.55
−3.39
−3.23
a)Calculated from the absorption band edge of the polymer film, Egopt = 1240/λedge b)Thin films in n-Bu4NPF6/CH3CN, versus ferrocene/ferrocenium at 100 mVs−1. HOMO
;
and LUMO estimated from the onset oxidation and reduction potentials, respectively, assuming the absolute energy level of ferrocene/ferrocenium to be 4.8 eV below
vacuum; c)
= hν – (Ecutoff – EHOMO), incident photon energy (hν = 21.2 eV) for He I.
UPS
EIP
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Figure 1. UV–Vis–NIR absorption spectra of DPP-TVT-n (n = 0, 1, 2). a) In dilute chloroform solution and b) as thin films on a quartz plate. c) Cyclic
voltammograms of the polymer films in n-Bu4NPF6/CH3CN solution (scan rate, 100 mVs−1). d) Ultraviolet photoelectron spectroscopy spectra of all
polymers. e) Calculated molecular orbitals and optimized geometries of the trimer oligomers.
DPP-TVT-1 and DPP-TVT-2, the temperature dependence was
not as intense as with DPP-TVT-0.
Consequently, with the aid of YFM, the Rc is extracted from
the transfer characteristics at very low drain voltage (VDS
–10 or 10 V) using Equations 1–5:
=
Aside from the flexibility in fabrication and better encap-
sulation effects resulting from the TG/BC configuration, the
top-gate structure is advantageous in achieving a relatively
low contact-resistance (Rc) in comparison with other bottom-
gated OFET geometry.[10] Consequently, this device con-
figuration was used, and the Rc effect of DPP-TVT-n OFETs
was explored by using the Y-function method (YFM) owing
to its unique features. This method offers a fast and accu-
rate way to evaluate the contact resistance, because only one
transfer sweeping for an individual transistor is required in
contrary to commonly used transfer-line method (TLM) with
various channel lengths. Therefore, the YFM is suitable for
extracting the contact resistance of individual transistors.
Although Rc in YFM method is supposed to be closely con-
stant with the gate voltage (VGS), of which assumption is
not actually matched to TLM, the values from YFM method
almost exist in the error ranges of TLM results proving its
accuracy.[11]
∂IDS
∂VGS
gm
=
(1)
(2)
VDS =const
IDS
W
Y =
=
( )
Ciμ0VDS × VGS −VT
gm
L
1
Sy =
(3)
(4)
gm
m(Sy)
m(Y)
θ =
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Figure 2. a) Hole and electron charge carrier mobilities for DPP-TVT-n (n = 0, 1, 2) semiconductors based on the annealing temperatures (150, 200, and
250 °C) (left panel: p-type and right panel: n-type characteristic). The summarized hole and electron b) charge mobilities, and c) channel-width normal-
ized contact resistances (RcW) for DPP-TVT-n OFETs at an annealing temperature of 200 °C, with the number of flanked thiophene units (n; n = 0, 1, 2).
θ
devices clearly demonstrated the largest electron contact resist-
ances of 6.07 × 105 Ω cm on average, as indicated in Figure 2c.
This steady increase in the electron contact resistances with
the number of flanked thiophene units can be ascribed to the
gradually high-lying LUMO energies (see Table 1). Conse-
quently, the relatively deep-lying LUMO energy (−3.55 eV) of
DPP-TVT-0 among three polymers, facilitated the most effi-
cient electron injection from the Au electrode owing to its low
injection barrier, resulting in the lowest electron contact resist-
ance amongst the OFETs. Correspondingly, together with a
structurally synergistic effect of combining fused DPP units
and vinylene linkages for their levels of co-planarity, the suit-
able positions of the LUMO energy levels of these DPP-TVT-n
polymers contributed to the effective electron charge injection
and transport. Therefore, the decreased number of electron-
donating thiophene spacer units (from 2 to 0) led to a noticeable
Rc =
(5)
[m(Y)]2 /VDS
where Ci is the capacitance of the gate dielectric per unit area,
gm is the transconductance, µ0 is the low-field mobility, θ is the
mobility attenuation factor, m(Sy) and m(Y) are the slopes of Sy
and Y (ordinates) against VGS (abscissa) respectively at strong
accumulation in linear regime. IDS and VT are the drain cur-
rent and the threshold voltage, respectively. Therefore, one can
extract the contact resistance by plotting the transconductance
(gm) versus the gate voltage (VGS) where the decreasing ten-
dency, namely the mobility attenuation factor (θ), incorporates
the influence of the contact resistance on the effective mobility.
As a result from YFM, the channel-width normalized con-
tact resistance (RcW) for electrons was found to be increased
with the addition of the thiophene units. The DPP-TVT-2
Table 2. Summary of the electrical OFET characteristics for DPP-TVT-T0, DPP-TVT-1 and DPP-TVT-2 in top-gate/bottom contact configurations at the
optimum annealing temperature (T = 200 °C).
a
Condition
Polymers
p-channel
n-channel
a)
a)
µh,max
[cm2 V−1s−1
µh,avg
Vth
[V]
µe,max
[cm2 V−1 s−1
µe,avg
Vth
[V]
]
[cm2 V−1 s−1
]
]
[cm2 V−1 s−1
]
DPP-TVT-0
DPP-TVT-1
DPP-TVT-2
0.37
2.96
1.88
0.78
0.36
0.04
55–60
55–70
61–68
0.26 ( 0.07)
1.89 ( 0.60)
1.50 ( 0.36)
−52 to −65
−52 to −77
−48 to −69
0.51 ( 0.11)
0.26 ( 0.07)
0.024 ( 0.014)
a)Standard deviations for charge mobilities are indicated in parentheses. All electrical characteristics were obtained from the top-gate based transistors more than ten.
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Figure 3. a) Transfer characteristics in the p-channel, and b) n-channel operation modes of DPP-TVT-n series ambipolar transistor devices (T = 200 °C).
a
The corresponding output characteristics of DPP-TVT-1 OFETs annealed at 200 °C for c) p- and d) n-type modes. (Channel length and width were
20 µm and 1000 µm, respectively.)
improvement in the electron mobilities. Consequentially, DPP-
TVT-0 exhibits high average balanced hole and electron mobili-
ties of 0.26 cm2 V−1 s−1 and 0.51 cm2 V−1 s−1, respectively. The
maximum mobilities for DPP-TVT-0 reached 0.37 cm2 V−1 s−1
for holes and 0.77 cm2 V−1 s−1 for electrons.
transport properties, grazing-incidence X-ray diffraction (GIXD)
experiments of both as-spun and annealed DPP-TVT-n thin
films were performed. The annealing temperatures of DPP-
TVT-0, DPP-TVT-1, and DPP-TVT-2 were all fixed at 200 °C,
at which each sample demonstrated the best electrical proper-
ties. For as-spun thin film samples DPP-TVT-0, DPP-TVT-1,
and DPP-TVT-2, first diffraction peaks (100) were observed
in X-ray scattering patterns (out-of-plane) at qz = 0.2898 Å−1,
0.2824 Å−1, and 0.3164 Å−1, with interlayer distances (d100) of
21.68 Å, 22.25 Å, and 19.86 Å, respectively (Figure S4∼S5). In
the all non-annealed samples, the interlayer and the (010) dif-
fraction attributing to π–π stacking peaks were observed at both
the out-of-plane and in-plane profiles, thus confirming a mix-
ture of face-on and edge-on orientations. An annealing-induced
improved crystallinity was observed for all polymers after
annealing at 200 °C; the films displayed higher intensity (100)
diffraction peaks and multi-peaks diffraction (see Figure 4).
Such an increase in long-range ordering could be an important
factor in the origins of their high mobilities upon annealing.
More interestingly, the (010) diffraction peaks were weakened
or disappeared at the out-of-plane GIXD profiles after annealing
(see Figure S4 for 1D-GIXD), especially in the annealed DPP-
TVT-1 and DPP-TVT-2 films, implying the favored orientation
change from the face-on structure to the edge-on structure. In
addition, atomic force microscopy (AFM) images indicated that,
after annealing at 200 °C, all polymer films were filled with
the uniformity that affords homogeneous structures. Notably,
the intertwined polymer fibers were observed for the annealed
DPP-TVT-2 film surfaces (see Figure S6).
However, the differences between the HOMO energies were
not very large in DPP-TVT-n semiconductors, exhibiting a
maximum difference of 0.15 eV between DPP-TVT-0, and DPP-
TVT-2. Alongside this tendency, the contact resistances for hole
injection in DPP-TVT-n were nearly consistently in the range
1.21 × 104?5.43 × 104 Ω cm; this was despite the DPP-TVT-1
and DPP-TVT-2 devices recording better average hole mobili-
ties of 1.89 and 1.50 cm2 V−1 s−1, respectively, in comparison
with DPP-TVT-0 (µh,avg = 0.26 cm2 V−1 s−1). The maximum hole
mobility, 2.96 cm2 V−1 s−1, was observed with DPP-TVT-1.
Figure 3 plots the representative transfer and output charac-
teristics of optimized DPP-TVT-based polymer OFETs and their
performances. Despite the similar HOMO levels and contact
resistances among the three polymers, the remarkably soaring
hole mobilities for DPP-TVT-1 and DPP-TVT-2 could have
arisen from the different solid-state ordering, degree of pla-
narity, and molecular packing properties in the polymer back-
bones at the semiconductor–insulator interfaces. Therefore, the
following section includes a discussion and comparison of the
semiconductor packing structures and their crystallite distribu-
tions in terms of their electrical performances through compre-
hensive X-ray analysis.
2.4. Microstructure Analyses
Furthermore, in the case of the annealed samples, as the
number of thiophene spacers in the backbone increased, both
(h00) diffractions representing lamellar packing and (010)
In order to gain a greater understanding of the correla-
tion between the crystalline microstructures and the charge
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Figure 4. Grazing incidence X-ray diffraction (GIXD) images of a–c) as-spun and d–f) annealed DPP-TVT-n (n = 0, 1, 2) thin films. The annealing
temperature of (d–f) were 200 °C. g) Proposed molecular packing of the DPP-TVT-n.
diffraction became more distinctively observed. Owing to the
charge transport/transfer being believed to be facilitated by
strong π–π stacking, the structures of DPP-TVT-1 and DPP-
TVT-2 having clear (010) diffraction can be considered as
favorable molecular conformation of high hole/electron trans-
port, in comparison with that of DPP-TVT-0. As schematically
illustrated in Figure 4g, it is postulated that the enhanced
lamellar packing and π–π stacking for both DPP-TVT-1 and
DPP-TVT-2 result from the large distances between DPP
motifs in a single repeat unit, thereby allowing the branched
side chains (2-octyldodecyl group) to pack properly along the
backbone without steric hindrance. Conversely, the reduced
distance arising from the absence of the thiophene spacers in
DPP-TVT-0 might perturb the alignment of the side chains to
the direction of the backbone, resulting in less ordered molec-
ular organization. Details of the layer spacing (d100) and π–π
stacking distance (d010) for the annealed films are summarized
in Table 3. Obviously, the shortest lamellar spacing and the
smallest π–π stacking distance for DPP-TVT-2 are observed,
indicating the more densely packed/ordered microstructure.
These intriguing results challenge the traditional assump-
tion that high carrier mobility is unambiguously linked to the
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Table 3. Crystallographic parameters of the annealed DPP-TVT-n (n =
0, 1, 2) thin films at the optimum annealing temperature (T = 200 °C).
a
a)
b)
c)
e)
d)
Polymer
d
[Å]
d
[Å]
L
[Å]
g
(h00)
[%]
(100)
(010)
(h00)
N
(h00)
DPP-TVT-0
DPP-TVT-1
DPP-TVT-2
20.87
20.91
19.53
3.89
3.84
3.80
103.0
144.9
202.0
4.9
4.9
3.8
4.0
7.0
10.7
a)Layer spacing (or domain spacing) of the plane; b)π–π stacking distance extracted
from in-plane direction; c)True paracrystal size normal to the (h00) plane; d)The
average number of the (h00) plane; e)The paracrystalline distortion parameter of
the (h00) plane.
degree of order, a paradigm that has been successfully used in
the past to describe charge transport in older semiconducting
polymers.[12]
In aiming to uncover the inconsistency between OFET
device performance and π–π stacking distances in the poly-
mers, distortion parameter and plane distribution were
examined. Paracrystals are known to be the building blocks
of many condensed matters, including polymers and biolog-
ical materials; consequently, assessment of the paracrystal-
line nature of the DPP-TVT-n thin films should prove quite
useful in correlating with charge transport properties. The
paracrystalline distortion parameter (g), defined as the sta-
tistical standard deviation from its average lattice position,
can be calculated from the slope (= g2π2/d; d is the domain
spacing) of the δb–h2 plot, where δb is the integral widths
of the diffraction peaks calculated from δb = 1/Lc (Lc: coher-
ence length or paracrystal size) and h is the order of dif-
fractions.[13] Furthermore, the true paracrystal size (LC) can
be obtained from the intercept of the straight line with the
ordinate. Additionally, the average number of the diffraction
2
N
plane (N) can be calculated from (LC) = d. The δb–h curves
of the annealed DPP-TVT-n thin films extracted from GIXD
data are included in Figure 5a and the crystallographic param-
eters are listed in Table 3. The calculated paracrystalline dis-
tortion parameter (g) values of DPP-TVT-0, DPP-TVT-1 and
DPP-TVT-2 were found to be 4.9, 3.8, and 4.0%, respectively.
Additionally, the average numbers of the diffraction plane
(N) of DPP-TVT-0, DPP-TVT-1 and DPP-TVT-2 were 4.9, 7.0,
and 10.7 layers, respectively.
An intensity-corrected pole figure plot along the (200)
diffraction peak of the annealed DPP-TVT-n thin films is
displayed in Figure 5b; these data imply the degree of dis-
tribution of (h00) plane. DPP-TVT-1 exhibited the narrowest
Figure 5. a) δb–h2 curves of the annealed DPP-TVT-n (n = 0, 1, 2) thin
films extracted from GIXD analysis. The error bar is the standard devia-
tion from a different set of measurements. b) Intensity corrected pole
figure plot along the (200) diffraction peak of the annealed DPP-TVT-n
(n = 0, 1, 2) thin films, where (200) the diffraction peak was chosen for
the pole figure plot in order to minimize the surface scattering effects
resulting from the substrate.
(h00) plane distribution (FWHM = 6.8°), while DPP-TVT-0 3. Conclusion
(FWHM = 12.4°) and DPP-TVT-2 (FWHM = 11.1°) exhibited
a distribution approximately two-times wider. When consid-
ering that DPP-TVT-1 has a relatively smaller paracrystalline
nature and narrower (h00) plane distribution, consisting of
With recent advances in the mobility of TVT-like polymers, a
systematic study of a tactical synthesized series of D–A poly-
meric hybrids (DPP-TVT-n) containing DPP and TVT, and the
different number of thiophene spacers was conducted with the
aim of establishing parallels and trends between TVT-based
structures and OFET performance. As demonstrated by optical
and electrochemical analyses, upon lowering the thiophene
content between DPP and TVT building blocks, the absorp-
tion spectra not only exhibited obvious red-shift, but a stepwise
increase in both LUMO and HOMO levels was also observed;
N
a moderate number of diffraction plane ( ≈ 7), in com-
parison with those of DPP-TVT-0 and DPP-TVT-2, this type
of molecular organization is regarded particularly favorable
for charge carrier. This is proposed to be the primary reason
for the observed highest hole mobility of DPP-TVT-1, despite
the aforementioned larger π–π stacking distance relative to
DPP-TVT-2.
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gold films. Film fabrication was performed in a N2-atmosphere glovebox.
The UPS analysis chamber was equipped with a hemispherical electron-
energy analyzer (Kratos Ultra Spectrometer), and the chamber was
maintained at 3.00 × 10−9 Torr. The UPS measurements were performed
using the He I (hν = 21.2 eV) source.
however, the LUMOs were clearly more easily affected. When
considering the size of the electron-donating moieties in the
polymer repeating unit, the variations in the energy levels of
the polymers do not follow a common tendency previously
observed in the literature. The utilization of the DPP-TVT-n in
OFETs leads to the achievement of ambipolar charge transport.
DPP-TVT-0 exhibited nearly balanced hole and electron mobili-
ties of 0.37 and 0.78 cm2 V−1 s−1, respectively. Of particular sig-
nificance is that OFETs based on the polymers, regardless of
the variation in LUMO levels, appeared to tune the polarity of
charge carriers with an increase in hole mobilities as they adopt
thiophene spacers, resulting in p-type dominant ambipolar
transport characteristics for DPP-TVT-1∼2. Among the poly-
mers, even though DPP-TVT-2 has the shortest value in both
lamellar d-spacing and π-stacking distance, DPP-TVT-1 demon-
strated the highest hole mobility (up to 2.96 cm2 V−1 s−1). Based
on the results in this study, it can be concluded that the degrees
of the paracrystalline nature and the (h00) plane distribution
also play a critical role in improving hole mobilities. These find-
ings should help not only to move towards the rationalization
of structure–property relationships in a relevant class of TVT-
like polymer semiconductors, but also to provide a new test
bench for charge-transport mechanisms, assisting in the design
of top-performing semiconducting polymers.
Morphology Analyses: Atomic force microscopy (AFM) images were
collected using a Digital Instruments dimension AFM system, controlled
by a nanoscope scanning probe microscope controller. Two-dimensional
Grazing incidence X-ray diffraction (2D-GIXD) measurements were
performed at the PLS-II 9A U-SAXS beamline of the Pohang Accelerator
Laboratory in Korea. The X-rays emitted from the in-vacuum undulator
(IVU) were monochromated (Ek = 11.09 keV, λ = 1.118 Å) using a
Si(111) double-crystal monochromator and were focused horizontally
and vertically (300 (H) µm × 30 (V) µm in FWHM at the sample
position) using a K-B type focusing mirror system. The GIXD sample
stage was equipped with a 7-axis motorized stage for the fine alignment
of the thin sample. The incidence angle of X-rays was adjusted to 0.10°,
which is just below the critical angle of DPP-TVT-n (n = 0, 1, 2). GIXD
patterns were recorded with a 2D CCD detector (Rayonix SX165, USA)
and the X-ray irradiation time was 10–20 s. The diffraction angle was
calibrated using pre-calibrated sucrose (Monoclinic, P21, a = 10.8631 Å,
b = 8.7044 Å, c = 7.7624 Å, β = 102.938°) and the sample-to-detector
distance was approximately 226 mm.[15]
Device Fabrication and Characterization: Top-gate/bottom-contact
geometry (TG/BC) was applied in the fabrication of the OFET devices.
Prior to the fabrication, the glass substrates (Corning Eagle XG) were
sequentially cleaned using acetone, isopropanol, and deionized water
for 10 min each using a sonication bath. The cleaned substrates
were dried in a vacuum oven at a temperature of 110 °C for 20 min.
Following this, the source and drain electrodes (Ni/Au = 3/13 nm) were
patterned through conventional photolithography processes and Ni and
Au were deposited on the glass substrates using thermal-evaporation
deposition. The resultant channel lengths were 10, 20, 30 and 50 µm
and the width was 1000 µm. The synthesized donor–acceptor DPP-
TVT-n polymers were used without further purification. The various
semiconductor solutions (DPP-TVT-0, DPP-TVT-1, and DPP-TVT-2)
from 5 mg mL−1 in 1,2,4-trichlorobenzene (from Sigma Aldrich) were
spin-coated at 1000 rpm for 30 s before being thermally annealed at
different temperatures within the range 150–250 °C for 30 min in a
N2-purged glove box. After thermal annealing of the semiconductors,
poly(methyl methacrylate) (PMMA; average Mw: 120kDa, purchased
from Sigma Aldrich) film was spin-coated from 80 mg mL−1 solution in
n-butyl acetate before being baked at 80 °C for 1 h in an N2-purged glove
box as gate dielectric layers with a thickness of ≈500 nm (capacitance:
6.20 nF cm−2). Finally, the transistors were completed by depositing
top-gate aluminum electrodes (≈50 nm) via thermal evaporation with
a metal shadow mask. Every OFET device was characterized using a
Keithley 4200-SCS semiconductor parameter analyzer connected to a
probe station in an inert N2-glove box.
4. Experimental Section
All chemicals materials were purchased from Aldrich and Alfa and were
used without further purification. All solvents were ACS and anhydrous
grade by distillation. 2-trimethylstannylthiophene, and 5-trimethylstannyl-
2,2′-bithiophene were synthesized according to a method reported
previously in the literature.[14] 1H NMR and 13C NMR spectra were
recorded using an Agilent 400 MHz spectrophotometer with CDCl3
being used as a solvent and tetramethylsilane (TMS) used as the internal
standard; MALDI MS spectra were checked using an Ultraflex III (Bruker,
Germany) system. UV–Vis–NIR spectra were recorded using a UV-1800
(SHIMADZU) spectrophotometer. DFT calculations were performed
using the Gaussian 09 package with the nonlocal hybrid Becke three-
parameter Lee-Yang-Parr (B3LYP) function and the 6–31G basis was set
to elucidate the HOMO and LUMO levels after optimizing the geometry
of DPP-TVT-0, DPP-TVT-1, and DPP-TVT-2 using the same method. The
number-average (Mn) and weight average (Mw) molecular weights, and
the polydispersity index (PDI) of the polymer products were determined
by performing gel permeation chromatography (GPC) with a Perkin-
Elmer Series 200 system using a series of mono disperse polystyrene
standards in THF (HPLC grade) at 313 K. Cyclic voltammetry (CV)
measurements were performed on (METEK, Versa STAT3) with a three-
electrode cell in 0.1 M tetra-n-butylammonium hexafluorophosphate
(n-Bu4NPF6) solution in acetonitrile, using a scan rate of 100 mV/s
at room temperature under nitrogen. Ag/Ag+, platinum, and glass
carbon were used as the reference electrode, counter electrode, and
working electrode, respectively. The Ag/Ag+ reference electrode was
calibrated using a ferrocene/ferrocenium redox couple as an internal
standard, with the oxidation potential set at −4.8 eV with respect to a
zero vacuum level. The HOMO energy levels were obtained from the
Synthesis of 2,5-bis(2-octyldodecyl)-3,6-di(thiophene-2-yl)pyrrolo[3,4-c]
pyrrole-1,4-dione (1):
A solution of 2-octyldodecyliodide (16.9 g,
41.6 mmol) was added dropwise to a mixture of 3,6-bis(thiophen-2-yl)-
2H,5H-pyrrolo[3,4-c]pyrrole-1,4-dione (5.0 g, 16.6 mmol), K2CO3 (5.75 g,
41.6 mmol) in anhydrous DMF (100 mL). The mixture was maintained
at 120 °C overnight. The reaction was cooled to room temperature and
evaporated under reduced pressure. The compound was extracted in
CH2Cl2, washed with brine, and dried over MgSO4. The crude product
was purified by chromatography on silica with 0–50% dichloromethane
in hexane used as an eluent. The isolated yield was 7.02 g (49%) as a
bright pink-red solid.
equation HOMO (eV) = – (E(ox)onset – E(ferrocene)onset + 4.8) and the LUMO
Synthesis
of
3-(5-bromothiophene-2-yl)-2,5-bis(2-octyldodecyl)-6-
onset
(thiophene-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (2): N-Bromosuccinimide
(NBS, 1.03 g, 5.80 mmol) in CHCl3 (100 mL) was added to a solution
levels were calculated from the equation LUMO (eV) = – (E(red)
–
onset
E(ferrocene)
+ 4.8). Ultraviolet photoelectron spectroscopy (UPS) was
of
2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2yl)pyrrolo[3,4-c]pyrrole-
examined using an AXIS-NOVA CJ109 system (Kratos). The polymer
solution was prepared in 5 mg mL−1 chlorobenzene for DPP-TVT-0,
DPP-TVT-1, and DPP-TVT-2. A gold film with a thickness of 75 nm was
deposited on a pre-cleaned Si substrate with a thin native oxide. The
DPP-TVT-0, DPP-TVT-1, and DPP-TVT-2 solutions were spin-coated onto
1,4-dione (1) (2 g, 2.32 mmol) at 0 °C over the course of 6 h. The
reaction was stirred at room temperature overnight and the solvent
was removed under reduced pressure. The crude product was purified
using chromatography on silica with 0–50% dichloromethane in hexane
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of the overlapping peaks. MALDI-TOF MS(m/z) 1023 (M+). Anal. calcd.
for C62H92N2O2S4: C, 72.60; H, 9.04; N, 2.73; O, 3.12; S, 12.51; found: C,
72.70; H, 8.98; N, 2.72; O, 3.01; S, 12.50.
utilized as the eluent. The isolated yield was 2.5 g (32%) as a bright
purple solid. 1H NMR (400 MHz, CDCl3, δ): 8.88 (d, J = 4 Hz, 1H), 8.61
(d, J = 4 Hz, 1H), 7.63 (d, 1H), 7.27 (d, J = 5.2 Hz, 1H), 7.22 (d, J =
4.4 Hz, 1H), 3.99–3.89 (m, 4H), 1.89–1.87 (m, 2H), 1.27–1.21 (m, 64H),
0.88–0.83 (m, 12H). 13C NMR (100 MHz, CDCl3, δ): 161.57, 161.43,
140.84, 138.89, 135.50, 135.02, 131.31, 131.27, 130.71, 129.76, 128.42,
118.53, 108.13, 107.76, 46.25, 37.74, 37.71, 31.92, 31.87, 31.32, 31.16,
30.05, 29.99, 29.63, 29.56, 29.54, 29.48, 29.35, 29.28, 26.33, 26.18,
22.68, 22.66, 14.10. MALDI-TOF MS(m/z) 937 (M+). Anal. calcd. for
C54H87BrN2O2S2: C, 68.97; H, 9.33; Br, 8.50; N, 2.89; O, 3.40; S, 6.82;
found: C, 68.69; H, 9.36; N, 2.88; O, 3.57; S, 6.55.
Synthesis of 3,6-bis(5-bromothiene-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]
pyrrole-1,4-dione (3): NBS (0.95 g, 5.34 mmol) was added slowly to a
solution of 2,5-bis(2-octyldodecyl)-3,6-di(thiophene-2-yl)pyrrolo[3,4-c]
pyrrole-1,4-dione (1) (1 g, 2.32 mmol) in CHCl3 (100 mL). The solution
was protected from light and stirred at room temperature overnight.
The reaction mixture was poured into water (100 mL) and extracted
in CHCl3. The organic layer was dried over MgSO4 and the solvent was
evaporated under reduced pressure. The crude product was purified by
chromatography on silica with 0–50% dichloromethane in hexane used
as an eluent. The isolated yield was 1.82 g (77%) as a purple solid. The
1H NMR assignment was in full agreement with that previously reported
one.[3h]
Synthesis of 2,5-bis(2-octyldodecyl)-3-(thiophen-2-yl)-6-(5-(thiophen-2-yl)
thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (4): 3-(5-bromothiophene-
2-yl)-2,5-bis(2-octyldodecyl)-6-(thiophene-2-yl)pyrrolo[3,4-c]pyrrole-
1,4-dione (2) (1.1 g, 1.17 mmol), 2-trimethylstannylthiophene (0.29 g,
1.17 mmol), tri(o-tolyl)phosphine (P(o-tolyl)3, 35.6 mg, 0.117 mmol) in
toluene (10 mL) were filled in a microwave reactor vial. After the mixture
was purged for 30 min, tris(dibenzylideneacetone)dipalladium(0)
(Pd2(dba)3, 53.5 mg, 0.058 mmol) was added to the solution mixture.
The mixture was heated at 100 °C for 1 h in a microwave reactor,
and reaction was cooled to room temperature. The solvent was
removed under reduced pressure. The crude product was purified by
chromatography on silica with 0–50% dichloromethane in hexane used
as an eluent. The isolated yield was 0.9 g (82%) as a purplish solid.
1H NMR (400 MHz, CDCl3, δ): 8.92 (dd, J = 3.2, 2.4 Hz, 2H), 7.59 (d,
J = 4.8 Hz, 1H), 7.30–7.27 (m, 3H), 7.25–7.22 (m, 1H), 7.06–7.03 (m,
1H), 4.01–3.89 (m, 4H), 1.95–1.91 (m, 2H), 1.29–1.21 (m, 64H), 0.87–
0.82 (m, 12H) ppm. 13C NMR (100 MHz, CDCl3, δ): 161.71, 161.55,
142.73, 139.97, 139.86, 136.70, 136.21, 135.13, 130.29, 129.92, 128.35,
128.20, 128.04, 126.18, 125.09, 124.69, 108.12, 108.09, 46.24, 37.92,
37.74, 31.92, 31.89, 31.32, 31.18, 30.05, 30.01, 29.64, 29.61, 29.55, 29.50,
29.36, 29.29, 26.34, 26.20, 22.69, 22.66, 14.11. MALDI-TOF MS(m/z)
941 (M+). Anal. calcd. for C58H90N2O2S3: C, 73.83; H, 9.61; N, 2.97; O,
3.39; S, 10.20; found: C, 73.57; H, 9.39; N, 3.12; O, 3.61; S, 10.56.
Synthesis of 2,5-bis(2-octyldodecyl)-3-(thiophen-2-yl)-6-(5-(5-(thiophen-
Synthesis
of
3-(5-bromothiophen-2-yl)-6-(5-(5-bromothiophen-2-yl)
(6):
thiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-dione
NBS (0.40 g, 2.23 mmol) was added slowly to a solution of 2,5-bis(2-
octyldodecyl)-3-(thiophen-2-yl)-6-(5-(thiophen-2-yl)thiophen-2-yl)
pyrrolo[3,4-c]pyrrole-1,4-dione (4) (1.0 g, 1.05 mmol) in CHCl3 (100 mL).
The solution was protected from light and stirred at room temperature
overnight. The reaction mixture was poured into water (100 mL) and
extracted in CHCl3. The organic layer was dried over MgSO4 and the
solvent was evaporated under reduced pressure. The crude product
was purified by chromatography on silica with 0–50% dichloromethane
in hexane used as the eluent. The isolated yield was 0.85 g (73%) as a
1
wine-color solid. H NMR (400 MHz, CDCl3, δ): 8.86 (d, J = 4 Hz, 1H),
8.61 (d, J = 3.6 Hz, 1H), 7.22–7.19 (m, 2H), 7.06 (dd, J = 4, 3.6 Hz, 2H),
3.99–3.91 (m, 4H), 1.90–1.88 (m, 2H), 1.29–1.21 (m, 64H), 0.88–0.83
(m, 12H) ppm. 13C NMR (100 MHz, CDCl3, δ): 161.37, 161.14, 141.56,
139.88, 138.54, 137.61, 136.74, 135.13, 131.28, 131.03, 130.61, 128.29,
125.06, 124.72, 118.62, 113.20, 108.16, 108.08, 46.27, 37.89, 37.74,
31.93, 31.89, 31.32, 31.18, 30.06, 30.00, 29.66, 29.57, 29.52, 29.38, 29.31,
26.34, 26.19, 22.69, 22.68, 22.51, 14.12. MALDI-TOF MS(m/z) 1098
(M+). Anal. calcd. for C58H88Br2N2O2S3: C, 63.25; H, 8.05; Br, 14.51; N,
2.54; O, 2.91; S, 8.73; found: C, 63.51; H, 8.05; N, 2.58; O, 2.75; S, 9.01.
Synthesis of 3-(5-bromothiophen-2-yl)-6-(5-(5-(5-bromothiophen-2-yl)
thiophen-2-yl)thiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-
dione (7): NBS (0.36 g, 2.05 mmol) was added slowly to a solution of
2,5-bis(2-octyldodecyl)-3-(thiophen-2-yl)-6-(5-(5-(thiophen-2-yl)thiophen-
2-yl)thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (5) (1.0 g, 0.975 mmol)
in CHCl3 (100 mL). The solution was protected from light and stirred
at room temperature overnight. The reaction mixture was poured into
water (100 mL) and extracted in CHCl3. The organic layer was dried
over MgSO4 and the solvent was evaporated under reduced pressure.
The crude product was purified by chromatography on silica with 0–50%
dichloromethane in hexane used as an eluent. The isolated yield was
0.9 g (78%) as a navy-color solid. 1H NMR (400 MHz, CDCl3, δ): 8.92
(d, J = 4 Hz, 1H), 8.61 (d, J = 4 Hz, 1H), 7.28 (d, J = 4 Hz, 1H), 7.20 (d,
J = 3.6 Hz, 2H), 7.05–6.93 (m, 3H), 3.95–3.90 (m, 4H), 1.88 (m, 2H),
1.330–1.22 (m, 64H), 0.87–0.82 (m, 12H) ppm. 13C NMR* (100 MHz,
CDCl3, δ): 161.43, 161.09, 142.29, 139.95, 138.27, 138.07, 137.06, 135.10,
134.09, 131.31, 130.82, 130.64, 128.11, 125.75, 124.68, 124.17, 118.51,
111.87, 108.23, 107.99, 46.27, 37.89, 37.74, 31.93, 31.89, 31.32, 31.18,
30.06, 30.00, 29.66, 29.57, 29.52, 29.38, 29.31, 26.34, 26.19, 22.69, 22.68,
22.51, 14.12. *All possible signals for the sp2 carbons were difficult to
detect separately, because of the overlapping peaks. MALDI-TOF
MS(m/z) 1180 (M+). Anal. calcd. for C62H90Br2N2O2S4: C, 62.92; H, 7.67;
Br, 13.50; N, 2.37; O, 2.70; S, 10.84; found: C, 62.87; H, 7.59; N, 2.17; O,
2.85; S, 10.76.
2-yl)thiophen-2-yl)thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione
(5):
3-(5-bromothiophene-2-yl)-2,5-bis(2-octyldodecyl)-6-(thiophene-
2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (2) (0.90 g, 0.957 mmol),
5-trimethylstannyl-2,2’-bithiophene (0.32 g, 0.957 mmol), P(o-tolyl)3 (29.1
mg, 0.096 mmol) in toluene (10 mL) were filled in a microwave reactor
vial. After the mixture was purged with argon for 30 min, Pd2(dba)3 (43.8
mg, 0.048 mmol) was added to the solution mixture. The mixture was
heated at 100 °C for 1 h in a microwave reactor, and reaction was cooled
to room temperature. The solvent was removed under reduced pressure.
The crude product was purified by chromatography on silica with 0–50%
dichloromethane in hexane used as the eluent. The isolated yield was
1.0 g (83%) as a dark purplish solid. 1H NMR (400 MHz, CDCl3, δ):
8.92 (dd, J = 3.6, 4 Hz, 2H), 7.61 (d, J = 4.4 Hz, 1H), 7.27 (s, 1H), 7.24
(s, 1H), 7.22 (t, J = 6.4 Hz, 2H), 7.12 (d, J = 4 Hz, 1H), 7.05–7.02 (t,
J = 9.2 Hz, 1H), 4.03–4.01 (m, 4H), 1.96–1.91 (m, 2H), 1.33–1.21 (m,
64H), 0.89–0.82 (m, 12H) ppm. 13C NMR* (100 MHz, CDCl3, δ): 161.73,
161.54, 142.39, 139.83, 138.23, 136.77, 136.66, 135.13, 134.74, 130.30,
129.93, 128.37, 128.01, 125.77, 125.09, 124.57, 124.54, 124.20, 108.16,
46.26, 37.96, 37.74, 31.92, 31.89, 31.36, 31.18, 30.08, 30.02, 29.69, 29.66,
29.59, 29.50, 29.37, 29.29, 26.39, 26.21, 22.69, 22.67, 14.12. *All possible
signals for the sp2 carbons were difficult to detect separately, because
Typical Procedure for Stille Polymerization and Polymer Purification:
Dibrominated DPP (3, 6, or 7) (0.196 mmol), trans-1,2-bis(tributylstannyl)
ethylene (0.196 mmol), P(o-tolyl)3 (19.6 µmol), and anhydrous toluene
(5 mL) were mixed in a Schlenk flask that had been purged with argon
for 30 min. To this solution, Pd2(dba)3 (9.81 µmol) was added and the
reaction was subsequently heated to 120 °C and stirred for 48 h. The
crude product was precipitated in methanol (200 mL). The precipitate
was collected into a Soxhlet thimble and sequential Soxhlet extraction
with methanol (1 day), acetone (1 day), hexane (1 day), and finally
chloroform (1 day) was performed. The final chloroform solution was
concentrated and precipitated in methanol. The final product was
filtered and drying in vacuo.
Synthesis of Poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]
pyrrole-1,4-dione)-alt-1,2-vinyl-5,5’-diyl) (DPP-TVT-0): The isolated yield was
120 mg (67%), Mn = 48.4 kDa, Mw = 96.6 kDa, PDI = 2.0. 1H NMR (600 MHz,
C2D2Cl4, δ): 8.93 (br, 2H), 7.01 (br, 4H), 4.09 (br, 4H), 1.97 (br, 2H), 1.25
(64H), 0.87 (br, 12H). Anal. calcd. for C56H88N2O2S2: C, 75.96; H, 10.02; N,
3.16; O, 3.61; S, 7.24; found: C, 75.75; H, 10.03; N, 3.12; O, 3.31; S, 7.25.
Synthesis of Poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]
pyrrole-1,4-dione)-alt-1-(2-thienyl)vinyl-5,5’-diyl) (DPP-TVT-1): The isolated
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Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201403527

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Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
D.Y. and B.N.-Y. contributed equally to this work. This research was
supported by the Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Korean Ministry of
Science, ICT, and Future Planning (Grant No.: 2013R1A1A1A05004475,
2010–0019408, BK21 Plus (10Z20130011057)). This research was also
supported by the International Cooperation of the Korea Institute of
Energy Technology Evaluation and Planning (KETEP) grant funded by
the Korean Ministry of Knowledge Economy (No. 20123010010140),
the Center for Advanced Soft-Electronics funded by the Ministry
of Science, ICT, and Future Planning as Global Frontier Project
(2013M3A6A5073183), and by the Dongguk University Research Fund of
2013. Experiments at the PLS-II 9A U-SAXS beamline were supported, in
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Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201403527
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