Oligothiophene quinoids containing a benzo[: C] thiophene unit for the stabilization of the quinoidal electronic structure

Article abstract of DOI:10.1039/c8tc01802b

Bis(dicyanomethylene)-substituted quinoidal π-conjugated systems possess a high electron-accepting nature and thus have been extensively investigated for application as n-type semiconductors. We focus on the utilization of benzene-annelation for the stabilization of the quinoidal electronic structure against the biradicaloid structure by designing quinoidal thiophenes 3-mer (BTQ) and 6-mer (BTQ-6) that have benzo[c]thiophene units. We also develop quinoidal oligothiophenes (BTQ-F) consisting of both benzo[c]thiophene and fluorinated thiophene units. The influence of benzo[c]thiophene on the quinoidal electronic structure is investigated by theoretical studies and property measurements. The molecular structure of BTQ-F is unambiguously confirmed through single-crystal X-ray diffraction. Analyses of cyclic voltammetry reveal that the lowest unoccupied molecular orbital energy levels of these compounds lie below -4.0 eV, leading to good electron-transporting characteristics even under ambient conditions in organic field-effect transistors (OFETs). Due to an increased highest occupied molecular orbital energy level, ambipolar transport is observed in BTQ-6, indicating the versatility of quinoidal π-conjugated systems incorporating benzo[c]thiophene.

Full text of DOI:10.1039/c8tc01802b

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Ie, M. Nitani, N. Tohnai, F. Kakiuchi, K. Zhang, W. Pisula, K. Asadi, P. Blom and Y. Aso, J. Mater. Chem. C,
2018, DOI: 10.1039/C8TC01802B.
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PAPER
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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Oligothiophene quinoids containing benzo[c]thiophene unit for
stabilization of quinoidal electronic structure
Keitaro Yamamoto,a Yutaka Ie,*a,b,e Masashi Nitani,a Norimitsu Tohnai,c Fumitoshi Kakiuchi,b,d Ke
Zhang,e Wojciech Pisula,e,f Kamal Asadi,e Paul W. M. Blom,e and Yoshio Aso *a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Bis(dicyanometylene)-substituted quinoidal -conjugated systems possess a high electron-accepting nature and thus have
been extensively investigated for application as n-type semiconductors. We focus on the utilization of benzene-annelation
for the stabilization of the quinoidal electronic structure against biradicaloid structure by designing quinoidal thiophene 3-
mer (BTQ) and 6-mer (BTQ-6) that have benzo[c]thiophene units. We also develop quinoidal oligothiophene (BTQ-F)
consisting of both benzo[c]thiophene and fluorinated thiophene units. The influence of benzo[c]thiophene on the
quinoidal electronic structure is investigated by theoretical study and property measurements. The molecular structure of
BTQ-F is unambiguously confirmed through single-crystal X-ray diffraction. Analyses of cyclic voltammetry reveal that the
lowest unoccupied molecular orbital energy levels of these compounds lie below –4.0 eV, leading to the good electron-
transporting characteristics even in ambient conditions in organic field-effect transistors (OFETs). Due to an increased
highest occupied molecular orbital energy level, ambipolar transport is observed in BTQ-6, indicating the versatility of
www.rsc.org/
quinoidal
-conjugated
systems
incorporating
benzo[c]thiophene.
attention as promising electron-transporting (n-type)
semiconductors.5-13 Another unique feature of the quinoidal
systems is an equilibrium between quinoidal and biradicaloid
Introduction
Significant research interest continues to focus on structurally
well-defined -conjugated oligomers, not only for the
electronic structures,14 which causes
a configurational

instability of quinoidal oligothiophenes. The representative
approach to increase the contribution of the quinoid
character in oligothiophenes is the utilization of aromatic
stabilization in a quinoidal form, which was accomplished by
the introduction of a fused aromatic ring on the thiophene
[c]bond, as observed in the first synthesis of
poly(isothianaphtene) with a small band gap by Wudl et al.15
In this context, quinoidal oligothiophenes containing
thieno[3,4-b]thiophene have been extensively developed by
Zhu et al.16 We envisioned that if the benzo[c]thiophene
elucidation of fundamental structure–properties relationship,
but also for the applications to organic thin-film electronics
such as organic field-effect transistors (OFETs) and organic
photovoltaics.1,2
-Conjugated compounds bearing quinoidal
structures have been extensively investigated not only as a
model structure of doped conducting arylene polymers, but
also as a Wurster-type multi-redox system in Hünig’s
classification.3 Among
them,
bis(dicyanomethylene)-
substituted quinoidal compounds, which generate anionic
aromatic state by accepting one or two electrons, exhibit a
high electron-accepting ability as for instance the well-known
tetracyano-p-quinodimethane.4 Therefore, the extension of
(isothianaphtene) quinoid unit can be incorporated into
-
extended quinoidal structures, the high aromatic stabilization
energy of this unit compared to that of benzo[c]thiophene
would allow us to create quinoidal oligothiophenes that have
potential as air-stable semiconducting materials. To pursue
this possibility, we designed new bis(dicyanomethylene)-
the
-conjugation of such quinoidal systems, typically
tetracyano quinoidal oligothiophenes, have attracted great
a.The Institute of Scientific and Industrial Research (ISIR), Osaka University, 8-1
Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
substituted quinoidal oligothiophenes (BTQ and BTQ-6
)
containing 5,6-dialkylbenzo[c]thiohene units (Fig. 1).
Furthermore, in order to increase the electron-accepting
ability of BTQ, fluorine substituents were introduced to the β-
positions of the quinoidal terthiophene (BTQ-F). In this
contribution, we report on the synthesis, properties,
structures, and OFET characteristics of these compounds.
Although parent bis(dicyanomethylene)benzo[c]thiophene
was synthesized and characterized by Cava et al. in 1993,17 its
b.Japan Science and Technology (JST) Agency, ACT-C, 4-1-8 Honcho, Kawaguchi,
Saitama, 332-0012, Japan.
c. Department of Materials and Life Science, Graduate School of Engineering, Osaka
University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
d.Department of Chemistry, Faculty of Science and Technology, Keio University, 3-
14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan.
e. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz,
Germany
f. Department of Molecular Physics, Faculty of Chemistry, Lodz University of
Technology, Zeromskiego 116, 90-924 Lodz, Poland
*Email - yutakaie@sanken.osaka-u.ac.jp
†Electronic Supplementary Information (ESI) available: the results of synthetic
details, NMR measurements, X-ray information, OFET device information, and

-extended derivative has not been reported so far.
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Fig. 1 a) Chemical structures of compounds investigated in this study. b) Calculated energy levels and orbitals for model compounds BTQ(Me) (left), BTQ-F(Me)
(center), and BTQ-6 (Me) (right). c) Chemical structures of reference compounds.
compounds is delocalized over the entire
-conjugated
backbone including the annelated benzene ring, which is
favorable for the intermolecular overlap of LUMOs between
neighboring molecules in the solid state.16b On the other
Results and discussion
Theoretical study. To estimate the molecular structure and
frontier orbital energies, we performed density functional
theory (DFT) calculation at the B3LYP/6-31G(d,p) level of
theory. All alkyl groups were replaced with methyl groups to
hand, the extension of -conjugation from BTQ(Me) to BTQ-
6(Me) mainly contributes to increasing the HOMO energy
level from –5.93 eV to –5.04 eV. The singlet biradical
character (y) of these qunoidal compounds was calculated by
the natural orbital occupation number of the lowest
unoccupied natural orbital with spin-unrestricted calculation
at the UHF/6-31G(d) level.18 Compounds BTQ(Me) and BTQ-
F(Me) gave y values of 0.36 and 0.39, respectively. As we
expected, these values were smaller when compared to that
of reference TQ(Me) (y = 0.45). Similarly, BTQ-6(Me) showed
a lower y value of 0.56 compared to that of TQ-6(Me) (0.75).
These results indicate that the introduction of the
benzo[c]thiophene unit is effective in increasing the
contribution of a quinoidal electronic structure in the ground
state.
ease the calculation. Optimized geometries of BTQ(Me), BTQ-
F(Me), and BTQ-6(Me) showed a planar conformation which
indicates that the introduction of the benzene annelation in
the central thiophene ring of terthiophene does not increase
the distortion with respect to the dihedral angle (Fig. 1(b)).
The lowest unoccupied molecular orbital (LUMO) energy level
of BTQ(Me) is higher compared to that of TQ(Me) (Fig.
1(b)(c)) but is still located at a low level of –4.01 eV. The
substitution of hydrogen atoms in the thiophene rings with
fluorine atoms for BTQ-F(Me) led to a further decrease of the
LUMO energy level to –4.23 eV, while maintaining a similar
highest occupied molecular orbital (HOMO)–LUMO energy
gap. It should be mentioned that the LUMO of both
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Scheme 1. Synthetic route of BTQ, BTQ-F, and BTQ-6.
Fig. 2 VT-NMR spectra of a) BTQ, b) BTQ-F, and c) TQ in aromatic regions in CDCl3. Signals pointed by asterisk are satellite peak of CHCl3.
Synthesis and Characterization. Since 5,6-dialkyl derivatives
of benzo[c]thiophene are not easily accessed from
5 prepared similarly to 4 is also shown in Scheme 1. Note that
2-ethylhexyl groups on the benzo[c]thiophene core are
essential to ensure proper solubility of the quinoidal
thiophene 6-mer. On the other hand, we cannot obtain pure
TQ-6 due to the low chemical stability. The chemical
commercially available compounds, we applied
a new
synthetic route, which relies on the construction of the
benzo[c]thiophene core from tetrasubstituted benzene
(Scheme 1). Methyl diester compound
1
was converted to 2-
structures of BTQ, BTQ-F, and BTQ-6 were fully characterized
pyridinyl ester , which was then reacted with Grignard
2
by NMR and MS. Detailed synthesis and characterization
were summarized in the ESI.
reagents, generated from 2-bromothiophene or 2-bromo-3,4-
difluoro-5-trimethylsilylthiophene, to give key intermediates
3a and 3b. Treatment of 3a and 3b with Davy’s reagent led to
the formation of the benzo[c]thiophene core, and the
obtained terthiophene derivatives were then treated with N-
bromosccinimide to afford 4a and 4b. Finally, palladium-
catalyzed coupling reactions of 4a and 4b with sodium
dicyanometanide, followed by oxidation with DDQ to give
BTQ and BTQ-F in 40% and 30% yield, respectively. The hexyl
groups in the benzo[c]thiophene moiety ensured the good
solubility of the molecules. The synthetic route of BTQ-6 from
In the 1H NMR spectrum of BTQ at 25 °C, two sets of
signals with an integration ratio of 10:1 were observed in the
aromatic region (Fig. 2),5a and all the peaks were assigned to
anti-anti and anti-syn isomers of the quinoidal terthiophene
backbone, respectively, by nuclear Overhauser effect
measurements (Fig. S1 in the ESI). On the other hand, almost
one singlet signal was observed for BTQ-F. In order to
investigate the isomerization behavior of BTQ, BTQ-F, and
TQ, variable temperature (VT)-NMR measurements were
performed at 0, 25, and 50 °C. As shown in Fig. 2, the spectra
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of BTQ and BTQ-F showed little temperature dependence.
Furthermore, the isomer ratio of BTQ is constant, irrespective
of the temperature. On the other hand, although the
spectrum of TQ showed two sets of signals at 0 °C similarly to
that of BTQ, the small peaks that originate from the anti-syn
isomer broadened at 25 °C and merged with the main peaks
at 50 °C, implying the equilibrium between the two isomers
provably via an aromatic biradical form. Similar anti–syn
equilibrium was also reported on tetracyano bithiophene
quinoid at 25 °C.19 These results indicate that the quinoidal
electronic structures of BTQ and BTQ-F are stabilized owing
to the reduced contribution of biradicaloid structure by the
benzene annulation. In addition, the presence of fluorine
atoms on the thiophene rings in BTQ-F induces not only steric
congestion in the syn form but also intramolecular S–F
attractive interactions, forming fixed anti configurations
between adjacent thiophene rings.20 In contrast, BTQ-6
showed broad signals even under the low temperature of –45
°C (Fig. S2), indicating the presence of equilibrium between
the isomers.
electronic interactions, the existence of biradical character
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may have influence on this bathochromDicOsIh: 1i0ft.1.039/C8TC01802B
Photophysical and Electrochemical Properties. UV-vis-NIR
absorption spectra of BTQ, BTQ-F, BTQ-6, and TQ in CH2Cl2
solutions are shown in Fig. 3, and the photophysical data are
summarized in Table 1. The absorption spectra of BTQ and
BTQ-F showed similar shapes with an absorption maximum
(λmax) at around 640 nm, which are slightly blue-shifted
compared to that of TQ (λmax = 670 nm) (Fig. 3(a)). These
intense bands are mainly assigned to the HOMO–LUMO
transition by time-dependent (TD)-DFT calculation at the
B3LYP/6-31G (d,p) level of theory (see the ESI). The
qualitative trend of molar extinction coefficients (ε) for these
compounds is in good accordance with estimated oscillator
strength. As summarized in Table 1, the optical HOMO–
LUMO energy gaps (ΔEgopt) of these compounds estimated
from the onsets in the absorption spectra are found to be ca.
1.7 eV. The absorption spectrum of BTQ-6 in a CH2Cl2 solution
exhibited an absorption band at the near-infrared region
(λmax = 978 nm) with a large ε of 2.6 × 105 M cm–1. This
behavior is in contrast to a previous report where quinoidal
sexithiophene showed a reduced molar extinction coefficient
with concomitant appearance of marked absorptions in the
visible region, compared to the corresponding quinoidal
quinquethiophene. The reduced extinction coefficient was
attributed to the high contribution of a biradical character,14b
which indicates that the high ε of BTQ-6 is rationalized by the
higher contribution of quinoidal electronic structure owing to
the presence of benzo[c]thiophene units in the framework.
Compared to the solution spectra, well-structured shoulders
with red-shifted λmax were observed for BTQ and BTQ-F in
thin films (Fig. 3(b)). This phenomenon is attributed to the
Fig. 3 a) UV-vis-NIR absorption spectra of BTQ (red) and BTQ-F (blue), TQ
(black), and BTQ-6 (green) in CH2Cl2 and b) in CH2Cl2 (solid line) and thin films
(dashed line).
The electrochemical properties of these compounds were
investigated by cyclic voltammetry (CV) measurements in
CH2Cl2
containing
0.1
M
tetrabutylammonium
hexafluorophosphate (TBAPF6) as a supporting electrolyte. All
potentials are calibrated against a ferrocene/ferrocenium
(Fc/Fc+) couple as a standard, and these values are listed in
Table 1. As presented in Fig. 4, the cyclic voltammograms of
BTQ, BTQ-F, and TQ showed one reversible oxidation and
reduction waves. The observed good reversibility indicates
the stable formation of both cationic and anionic species.
Integration of each peak area for these compounds implied
the participation of one electron and two electrons in
oxidation and reduction processes, respectively. As shown in
Table 1, due to the electron-withdrawing nature of fluorine
atoms, both half-wave oxidation potential (Eox
) and
1/2
reduction potential (Ered1/2) of BTQ-F are positively shifted
compared to those of BTQ. Under the assumption that the
energy level of Fc/Fc+ is −4.8 eV below the vacuum level,21-23
the LUMO energy levels (ELUMO) of BTQ and BTQ-F were
estimated to be –4.06 and –4.30 eV, respectively. These
values are in good agreement with those estimated from the
theoretical calculation. For BTQ-6, two reversible oxidation
and reduction processes were observed. The ELUMO and EHOMO
intermolecular electronic interactions of
− stacked
backbones, which are favorable for carrier transport in thin-
film devices. The absorption spectrum of BTQ-6 in thin film
showed a broad absorption with the onset reaching 1800 nm.
Such a large bathochromic shift was observed for quinoidal
quarterthiophene.9 In addition to the intermolecular
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of BTQ-6 estimated from the first Ered1/2 and Eox1/2 were −4.26
and −4.88 eV, respectively, indicating that the extension of
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DOI: 10.1039/C8TC01802B
the quinoidal
-system leads to a significant rise of the
HOMO energy level. This qualitative trend of HOMO and
LUMO energy levels is also in good agreement with
theoretical estimation.
Table 1. Photophysical and electrochemical properties.
opt
Comp
ound
BTQ
BTQ-F
BTQ-6
λmax (ε × 105)
/nm (M cm–1)a)
642 (0.9)
636 (1.0)
978 (2.6)
ΔEg
Eox
Ered
EHOMO
/eV c)
–5.66
–5.85
–4.88
ELUMO
/eV d)
–4.06
–4.30
–4.26
1/2
1/2
/eV a)
1.70
1.71
1.14
/V b)
0.86
1.05
0.08
0.35
0.81
/V b)
–0.74
–0.50
–0.54
–0.61
–0.58
TQ
670 (1.1)
1.60
–5.61
–4.23
a) In CH2Cl2. b) In CH2Cl2 containing 0.1 M TBAPF6. V vs Fc/Fc+. c) EHOMO = –Eox
4.8. d) ELUMO = –Ered 1/2–4.8.
–
1/2
Fig. 5 a) ORTEP drawing of molecular structure, b) packing diagram from side
view (top) and top view (bottom), and c) estimated transfer integrals of
HOMOs and LUMOs for BTQ-F
.
Charge Carrier Transport and Film Morphologies. To
evaluate the semiconducting charge-transport characteristics
of BTQ, BTQ-F, BTQ-6, and TQ, OFET devices based on thin
films were fabricated. Although there have been several
reports on high or finely tuned ambipolar OFETs of ter- and
quater-thiophene quinoids,5 the compounds in this work
were characterized by using a conventional bottom-gate
bottom-contact transistor configuration with similar
fabrication conditions for all devices. The active layer was
prepared by spin-coating from a 0.3 wt% CHCl3 solution onto
hexamethyldisilazane (HMDS)-modified Si/SiO2 substrates.
Thermal annealing was effective for improving the
performance for BTQ and BTQ-F, and the current–voltage
characteristics of best-performance devices are shown in Fig.
6, S3, and S4. The hole (μh) and electron mobilities (μe) were
extracted from the transfer characteristics at constant
source–drain voltages. The corresponding device parameters
as mobility, threshold voltage (Vth), and current on/off ratio
(Ion/Ioff) are summarized in Table 2. Both BTQ and BTQ-F
revealed solely an electron transport with μe in the order of
10–3 cm2 V–1 s–1 due to their low-lying LUMO energy levels.
Furthermore, OFETs based on these compounds retained the
Fig. 4 Cyclic voltammograms of a) BTQ (red) and BTQ-F (blue), TQ (black), and
BTQ-6 (green) in CH2Cl2 containing 0.1 M TBAPF6.
X-Ray Single-Crystal Structures. The structure of BTQ-F was
unambiguously determined by using X-ray crystallographic
analysis of the crystals that were grown by the slow
evaporation from a solution in ethyl acetate (EtOAc) and
MeOH mixed solvent. As shown in Fig. 5(a), the molecular
structure of BTQ-F adopts all anti and planar conformation
with dihedral angles of less than 2.7°. On the other hand, the
distance of the intramolecular S–F contact (2.75 Å) is smaller
than the sum of van der Walls radii of S and F atoms (3.27 Å),
indicating the presence of nonbonding attractive interactions
between these atoms. In the packing diagram, BTQ-F
molecules are oriented in a face-to-face fashion with the
minimum intermolecular – distances of 3.55 Å and 3.42 Å
same order of μe under air-exposed conditions. While the TQ
-
(a and b in Fig. 5(b), respectively). On the basis of the
calculation by the Amsterdam Density Functional program at
the PW91/TZP level, the transfer integrals between facial
stacked structures of BTQ-F in the crystal were estimated. All
the transfer integrals for electron transport (tLUMO) and hole
transport (tHOMO) are summarized in Fig. 5(c). BTQ-F showed a
large tHOMO and tLUMO of 75.5 and 99.9 meV, respectively,
which is expected to construct charge-carrier transporting
pathway along the stacking direction.
based device exhibited higher µe compared with BTQ and
BTQ-F, the Ion/Ioff ratio was quite low due to a high off
source–drain current (Fig. S4(d)). This might indicate that the
ambipolar character of TQ framework effects the increase of
carrier density even in the off state.6b
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Table 2. Field-effect characteristics under vacuum and in air
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DOI: 10.1039/C8TC01802B
compoundsa)
Anneal
temp. /°C
170
170
170
170
As cast
150
As cast
(As cast) c)
Vth /V
Ion/Ioff
μe /cm2 V–1 s–1
(μh /cm2 V–1 s–1)
3.4 × 10–3
BTQ a)
BTQ b)
BTQ-F a)
BTQ-F b)
TQ a)
TQ b)
BTQ-6
15
18
13
–9.4
35
22
104
105
2.5 × 10–3
105
1.2 × 10–3
103
3.0 × 10–4
101
3.3 × 10–2
102
3.4 × 10–2
78
(–29) c)
101
8.9 × 10–4
(102) c)
(3.1 × 10–2) c)
a) Under vacuum. b) In air. c) Hole-transporting characteristics are shown in
parenthesis.
Fig. 6 a) Transfer characteristics of OFETs using a) BTQ, b) BTQ-F, c) BTQ-6, and
d) BTQ-6. VGS, ISD, and VSD denotes gate voltage, source–drain current, and
source–drain voltage, respectively.
In order to investigate the film properties of these
compounds, X-ray diffraction (XRD) and atomic force
microscopy (AFM) measurements of these thin films on
HMDS-modified Si/SiO2 substrates were performed. As
shown in Fig. 7 and S5, these compounds exhibited clear
diffraction peaks in X-ray diffractogram (XRD), indicating the
formation of crystalline structures in thin films. The peak of
BTQ-F at 2= 6.2° can be indexed as a (011) diffraction peak
with a d spacing of 14.2 Å according to the above-mentioned
X-ray crystal structure analysis. Thus, the BTQ-F molecules
are edge-on arranged with the stacking direction parallel to
the SiO2 surface. While AFM image of BTQ revealed crystal-
shaped micrometer-sized grains, BTQ-F showed a rough film
surface with large crystal grains (Fig. 7). Both BTQ and BTQ-F
maintained OFET responses under air-exposed conditions,
irrespective of the difference of the film morphologies. This
result indicates that the observed air-stability mainly
originates from the thermodynamic stability, i.e, low LUMO
energy level of less than −4.0 eV. As discussed above, the
introduction of benzene annelation led to the isomerization
behavior different from that of TQ against temperature
change. Therefore, to investigate the influence of the
benzene annelation on the device characteristics,
temperature-dependent OFET measurements of BTQ- and
TQ-based devices were performed. For these measurements,
we performed the surface modification of the source and
drain gold electrodes using hexadecanethiol to minimize the
contact resistance between Au electrodes and active layer.24
The decreased contact resistance was confirmed by the
output characteristics (Fig. S6).
Fig. 7 AFM height images and XRD data of a) BTQ and b) BTQ-F
.
As shown in Fig. 8(a), OFETs using BTQ showed a decrease
of electron mobility with decreasing the temperature. This
phenomenon is in agreement with the temperature
dependence of hopping dominated carrier transport.25 The
activation energy of BTQ was estimated to be 0.13 eV (Fig.
S7). On the other hand, the TQ-based device showed a
reverse trend with a decrease in off current (Fig. 8(b)). We
speculate that the diminution of the biradical character for
BTQ might facilitate the inherent electron transport, which
means that biradicals act as both carriers. Although the
presence of the sterically bulky 2-ethylhexyl groups may
prevent dense
– stacking, XRD results indicate the
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that
quinoidal
-conjugated
systems ViewcAortinclteaOinnilninge
DOI: 10.1039/C8TC01802B
crystalline structures in thin films (Fig. 7(c)). In fact, OFET
devices based on BTQ-6 showed not only an electron-
transporting characteristics (8.9 × 10–4 cm2 V–1 s–1) but also
hole-transporting characteristics (3.1 × 10–2 cm2 V–1 s–1). The
appearance of p-type behavior can be explained by the
increased HOMO energy levels. Note that the field-effect
response for the quinoidal thiophene 6-mer is not reported
benzo[c]thiophene units have potential as candidates for
semiconducting materials using stabilized quinoidal structures.
Further investigations toward expansion of the -conjugation are
currently underway in our group.
Conflicts of interest
There are no conflicts to declare.
so far. The OFET devices based on BTQ, TQ, and BTQ-6 were
stored and measured periodically under the air-exposed
condition. As shown in Fig. S8, compared to TQ, a decrease of
carrier mobility is suppressed for benzo[c]thiophene-
containing semicondutors. We have considered that the
introduction of the benzene annelation to form a stabilized
quinoidal electronic structure becomes an effective strategy
in developing new semiconducting materials.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific
Research (B) (16H04191) and Innovative Areas (JP25110004)
and "Dynamic Alliance for Open Innovation Bridging Human,
Environmental and Materials" from The Ministry of
Education, Culture, Sports, Science and Technology, Japan
and ACT-C programs from the Japan Science and Technology
Agency Japan. Thanks are extended to the Comprehensive
Analysis Center (CAC), ISIR, for assistance in obtaining
elemental analyses and HRMS.
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