Synthesis and Physicochemical Properties of Dibenzo[2,3- d:2′,3′- d′]anthra[1,2- b:5,6- b′]dithiophene (DBADT) and Its Derivatives: Effect of Substituents on Their Molecular Orientation and Transistor Properties

Article abstract of DOI:10.1021/acs.joc.8b02557

We have synthesized dibenzo[2,3-d:2′,3′-d′]anthra[1,2-b:5,6-b′]dithiophene (DBADT) and several derivatives bearing alkyl and phenyl groups at various positions. The optical and electrochemical properties of the synthesized compounds were investigated. All

Full text of DOI:10.1021/acs.joc.8b02557

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Article
Synthesis and Physicochemical Properties of Dibenzo[2,3-d:2',3'-
d']anthra[1,2-b:5,6-b']dithiophene (DBADT) and Its Derivatives: Effect of
Substituents on Their Molecular Orientation and Transistor Properties
Keita Hyodo, Shuhei Nishinaga, Yuta Sawanaka, Takumi Ishida, Hiroki Mori, and Yasushi Nishihara
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b02557 • Publication Date (Web): 18 Dec 2018
Downloaded from http://pubs.acs.org on December 23, 2018
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Synthesis and Physicochemical Properties of Dibenzo[2,3-d:2’,3’-
d’]anthra[1,2-b:5,6-b’]dithiophene (DBADT) and Its Derivatives:
Effect of Substituents on Their Molecular Orientation and Transistor
Properties
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Keita Hyodo,† Shuhei Nishinaga,† Yuta Sawanaka,† Takumi Ishida,†
Hiroki Mori,‡ and Yasushi Nishihara*,‡
†Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and
Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
‡Research Institute for Interdisciplinary Science, Okayama University, 3-1-1 Tsushimanaka,
Kita-ku, Okayama 700-8530, Japan
Table of Contents
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ABSTRACT. We have synthesized dibenzo[2,3-d:2',3'-d']anthra[1,2-b:5,6-b']dithiophene
(DBADT) and several derivatives bearing alkyl and phenyl groups at various positions. The
optical and electrochemical properties of the synthesized compounds were investigated. All
the fabricated OFET devices exhibited typical p-type behavior under ambient conditions, and
diphenyl-substituted analogue-based OFET devices showed excellent mobility, as high as
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0.66 cm2 V s . The surface morphology and molecular orientation in thin films were also
investigated using atomic force microscopy (AFM) and two-dimensional grazing incidence
X-ray diffraction (2D-GIXD). It was found that the substituents and their positions affect the
molecular orbitals, molecular orientation, and morphology of the thin films, producing
different FET performance.
Introduction
Organic semiconducting materials with highly extended -electron systems have been
widely used in organic electronic devices, such as organic field-effect transistors (OFETs),
organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs).1 In particular,
integrated circuits based on OFETs have been recognized as important components that can
play a key role in organic electronics, because they are needed to operate active-matrix
displays, sensors, and RF-ID tags. Polycyclic aromatic hydrocarbons (PAHs) are one of the
potential high-performance OFET materials.2 For instance, linearly extended pentacene and
picene derivatives are representative high-performance p-type semiconductors, which
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respectively showed high mobilities of up to 3 cm2 V s and 20.9 cm2 V−1 s−1 4. However,
the former is unstable and easily deteriorates under ambient conditions due to its high HOMO
energy level of 5.0 eV.5 The latter exhibited an extremely high threshold voltage owing to
its deep HOMO energy level of −5.5 eV, 6 which often prevents smooth hole injection.7
Thienoacenes, which are sulfur-containing polycyclic aromatic compounds, are also
promising candidates for high-performance materials for the following reasons. First, the
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large atomic radius of sulfur atoms can enhance the extent of their interaction, leading to
more effective π-orbital overlaps intermolecularly.8 Second, the thienoacenes can extend
their π-conjugation and construct a pseudo-linear structure without significant elevation of
their HOMO energy level, resulting in low-voltage device operation.9 Third, a thiophene ring
is easier to construct than a benzene ring. Recent synthetic progress has yielded many types
of ring-closing reactions for the preparation of thiophene rings, and it has become possible to
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synthesize highly extended thienoacenes.10
In these efforts, numerous thienoacenes
involving [1]benzothieno[3,2-b]benzothiophene (BTBT) analogues,11 dinaphtho[2,3-b:2’,3’-
d]thiophenes (DNT-Vs),12 and dinaphtho[2,3-d:2’,3’-d’]benzo[1,2-b:4,5-b’]dithiophenes
(DNBDTs)13 have been developed, with hole mobilities reaching over 5 cm2 V−1 s−1.
Two strategies in the hunt for high-performance thienoacene-based OFETs are 1)
expansion of -electron systems and 2) introduction of alkyl or aromatic groups.10,14 For
instance, C10-DNBDT with seven fused aromatic rings showed excellent hole mobility of up
to 16 cm2 V−1 s−1,13 which is higher than that of the related five ring-fused molecules, C6-
DNT-VW (µFET = 9.5 cm2 V−1 s−1).12 Such π-extension can enhance the intermolecular
electronic coupling due to large π-planes, which lead to a dense packing structure in the solid
state. Additionally, the introduction of long alkyl chains or aromatic rings has shown another
promising way. In the study of dinaphtho[2,3-b:2’,3’-f’]thieno[3,2-b]thiophene (DNTT)
derivatives, as reported by Takimiya and coworkers, DNTT-based OFET devices exhibited
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high mobility of up to 2.9 cm2 V s1,15a while dialkylated-DNTT-based devices displayed a
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further enhanced mobility of up to 8.0 cm2 V s1 15b owing to the fastener effect, which can
lead to a tight packing structure through van der Waals intermolecular interactions between
alkyl chains.15c,15d Moreover, diphenyl-bis[1]benzothieno[2,3-d;2’,3’-d’]naphtho[2,3-b;6,7-
b’]dithiophene (DPh-BBTNDT) also has higher hole transport ability (µFET = 7.0 cm2 V−1 s−1)
than that of the parent BBTNDT, which resulted in its increased transfer integral and more
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isotropic electronic structure.16 However, the position of substituents strongly affects the
packing structure and thus the OFET performance, particularly along the molecules’ long
axis.17 Thus, the introduction of long alkyl chains or aromatic rings at the optimal position is
highly important for the development of high-performance thienoacenes.
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Previously, we have developed various phenacene-type molecules via Lewis acid-
catalyzed cycloaromatization.18 21
In particular, 2,7-didodecyl-phenanthro[2,1-b:7,8-

b’]dithiophene (C12-PDT-2) exhibited excellent mobility of up to 5.6 cm2 V s with a
PbZr0.52Ti0.48O3 (PZT) gate dielectric with a high k value.20 Although our developed
materials displayed better mobilities, the absolute threshold voltages bear high values due to a
large energy barrier between the work function of gold (~5.1 eV) as source and drain
electrodes and the HOMO energy levels of the active layer (5.6 ~ 5.8 eV). In order to
solve this problem, we have recently developed a material with nine fused aromatic rings,
bis[1]benzothieno[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-b’]dithiophene (BBTADT), incorporating
an acene moiety in its molecular center, which increases its HOMO energy level, leading to
smooth hole injection from the gold electrodes.22 Fabricated OFET devices showed the low-
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voltage operation (|Vth| = 9 V), although the highest mobility was only 2.7  10 cm2 V s
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due to its unfavorable solid state structure. One of the reasons for the low mobility is the
unsuitable HOMO geometry, indicating that the sulfur atoms are completely in the nodal
plane, which would reduce intermolecular orbital overlaps.10 To overcome these drawbacks,
we newly designed dibenzo[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-b’]dithiophene (DBADT) and its
alkyl and phenyl-substituted derivatives. From DFT calculations (Figure 1), DBADT’s
HOMO has a large electron density on the sulfur atoms, which can thus form efficient π-
orbital overlaps between neighboring molecules in the solid state. In addition, such effective
intermolecular interaction may provide a dense packing structure, leading to highly ordered
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crystalline films. Herein, we report the synthesis and characterization of a series of DBADT
derivatives, and discuss the effect of the substituents and their positions on FET performance.
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Figure 1. Molecular structures and HOMO orbitals of BBTADT and DBADT derivatives.
Results and Discussion
Synthesis of DBADT and Its Derivatives. A subsequent synthetic route to DBADT
derivatives 5a-5e is summarized in Scheme 1. Palladium-catalyzed Suzuki-Miyaura coupling
of commercially available 2-benzothienylboronic acid (1a) and 2 afforded dialdehyde 3a in
96% yield. Accordingly, dialdehydes 3b-3e bearing various substituents were synthesized
with excellent yields through palladium-catalyzed Negishi coupling of 2 with 2.2 equiv of the
23
corresponding zinc reagents, derived from deprotonation and the subsequent zincation of
benzo[b]thiophene derivatives 1b-1e. The subsequent epoxidation of 3a-3d afforded the
corresponding epoxides 4a-4d in high yields. However, epoxidation of 3e in acetonitrile did
not afford the epoxide 4e because of its low solubility. To our delight, we could successfully
synthesize 4e by epoxidation of 3e in benzonitrile as the solvent. Finally, DBADT
derivatives 5a-5e were obtained in 78-91% yields through indium-catalyzed Friedel-Crafts-
type intramolecular double cycloaromatization.24 DBADT derivatives 5a-5e showed quite
low solubility in common organic solvents such as THF, toluene, chloroform, and even
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chlorobenzene. Since our synthetic method does not yield any structural isomers of DBADT
upon cycloaromatization, the purity of DBADT derivatives was confirmed by elemental
analyses.
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Scheme 1. A synthetic route to DBADT derivatives
Optical and Electrochemical Properties. To investigate the optical properties of DBADT
derivatives 5a-5e, we next measured UV-vis absorption spectra in CH2Cl2 solution and thin
films, which are shown in Figure 2, and the corresponding optical data is summarized in
Table 1. The thin films were prepared by vapor deposition at the rate of 0.1 Å/s on a quartz
glass substrate. Molar absorption coefficients of all DBADT derivatives were not determined
due to their low solubility. The maximum absorption wavelength of DBADT 5a in solution
was observed at 327 nm, which is ca. 20 nm red-shifted relative to that of anthra[1,2-b:5,6-
b’]dithiophene (ADT, λmax = 304 nm),25 due to its extended π-conjugation. Dialkylated
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derivatives 5b and 5c showed similar absorption maxima of 331 nm and 333 nm, respectively.
Accordingly, their HOMO-LUMO energy gaps (2.89 eV for 5b and 5c) were slightly smaller
than that of 5a (2.92 eV), indicating that any substitution position effect on the electronic
structure is negligible when alkylating DBADT. One possible reason for the slight alkylation
effect on electronic structure may be the weak electron-donating nature of alkyl groups. The
absorption maximum of diphenylated derivative 5d was also shifted bathochromically by 15
nm and the energy gap of 5d (2.86 eV) was smaller than that of 5a owing to the additional
aromatic groups incorporated, which led to the extended π-conjugation. On the other hand,
the absorption maximum of diphenyl-substituted DBADT 5e at 4,12-positions was blue-
shifted by about 7 nm compared with that of 5d. In addition, the optical energy gap of 5e
(2.90 eV) is almost same as that of 5a, indicative of no extension of π-conjugation. This
result might come from the coefficients of the highest occupied molecular orbitals (HOMO).
DFT calculations indicate that the HOMO coefficients of 5d are delocalized over the entire
molecule, including the introduced benzene rings. In contrast, the HOMO coefficients of 5e
are completely localized on the DBADT framework, because the 4,12-positions of a DBADT
core are nodal planes in HOMO geometry (Figure S1). These results indicate that the
introduction of benzene rings at the 3,11-positions of the DBADT core affects the electronic
structure of DBADT, whereas the installation of phenyl groups at 4,12-positions has little
effect on the electronic state of DBADT. According to the absorption spectra in thin films,
the absorption maxima of 5a-5e were bathochromically shifted at around 432-442 nm
compared to their longest absorption wavelength in solution, indicating that they have a
highly ordered packing structure in the solid state.
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Furthermore, we used cyclic voltammetry (CV) to investigate the electrochemical
properties of DBADT derivatives 5a-5e. Figure S2 shows the cyclic voltammograms of 5a-
5e, and their electrochemical data are also listed in Table 1. Three DBADT derivatives, 5a-
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5c, showed one oxidation wave with a clear reduction process, while 5d showed no oxidation
wave due to its low solubility in CH2Cl2, caused by the introduction of benzene rings onto the
DBADT framework. In contrast, 5e displayed a reversible oxidation process, which indicates
that the substitution positions of benzene rings affect the solubility, likely due to different
dihedral angles between phenyl rings and the DBADT core. The estimated HOMO energy
levels of 5a-5e were 5.43 ~ 5.50 eV below the vacuum level from the onset of oxidation
peaks, which indicates that the introduction of alkyl or phenyl groups onto a DBADT
framework elevates the HOMO energy levels slightly, but no significant trend was observed.
These results suggest that the fabricated OFET devices based on DBADT derivatives 5a-5e
can be expected to have high air stability.
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Figure 2. UV-vis absorption spectra of 5a-5e in CH2Cl2 solution (solid line) and thin films
(dashed line).
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Table 1. Optical and Electrochemical Data of 5a-5e
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abs,sol
abs,film
opt
λmax
(nm)a
λmax
(nm)
Eg (eV)b
EHOMO
(eV)c
ELUMO
(eV)d
Compound
/λedge (nm)
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5a
5b
5c
5d
5e
327
331
333
342
335
432
432
433
442
442
2.97/417
5.50
5.45
5.43
NDe
2.53
2.53
2.52
NDe
2.92/424
2.91/426
2.90/427
2.96/419
5.46
2.50
5
aAbsorption maxima in the CH2Cl2 solution (1 × 10 M). Estimated from the absorption
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c
d
edge (λedge). Estimated from: EHOMO = 4.80  Eonset. Calculated according to the formula:
opt
ELUMO = EHOMO + Eg
.
eEonset was not determined by cyclic voltammetry due to the low
solubility of 5a-5e.
FET Characteristics. To investigate the FET characteristics, we next fabricated bottom-
gate/top-contact OFET devices based on DBADT derivatives 5a-5e with an Si/SiO2 substrate.
The surfaces of the Si/SiO2 substrates were modified with n-octyltrichlorosilane (OTS) or n-
octadecyltrichlorosilane (ODTS) as a self-assembled monolayer (SAM). Active layers of 5a-
5e were prepared by vapor deposition at a rate of 0.1 Å/s, and sequential thermal annealing
processes were performed at 100, 150, and 200 °C for 30 min under an inert atmosphere in
order to form a highly ordered packing structure in the thin films. The gold source and drain
electrodes were applied through a shadow mask by vacuum deposition, which gave a channel
length (L) of 100 μm and a width (W) of 2 mm. Measurement of FET characteristics was
carried out under ambient conditions in the dark. The best hole mobilities for each compound
under the optimized FET parameters are summarized in Table 2, and the corresponding
transfer and output characteristics are shown in Figures 3 and S3, respectively. Hole
mobilities were compensated by the ideal Shockley equations.26 All the fabricated devices
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exhibited typical p-channel characteristics, and DBADT 5a-based OFET devices exhibited a
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high hole mobility of 0.37 cm2 V s on OTS-treated Si/SiO2 substrate. However, the
mobilities of dialkyl-substituted DBADT 5b and 5c were lower than that of 5a. These results
indicated that the introduction of alkyl chains onto the DBADT core does not induce the
higher mobility by a fastener effect. Although the highest mobility of 5d-based OFET
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devices was 0.08 cm2 V s , which is about five times lower than that of 5a, to our delight,
5e-based OFET devices displayed the highest hole mobility of up to 0.66 cm2 V s ,
indicating that the introduction of phenyl groups at the 4,12-positions of the DBADT core
could enable effective carrier transport in OFET devices due to the resulting surface
morphology, high crystallinity and molecular orientation in thin films (vide infra).
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Figure 3. Transfer characteristics of fabricated OFET devices based on DBADT derivatives
5a-5e.
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Table 2. FET Characteristics of OFET Devices Based on 5a-5e
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a,b
μ/cm2 V s
Compound
SAM
OTS
Ta/ºC
150
Vth/Vb
Ion/off
5a
5b
5c
5d
5e
0.37 (0.26)
0.32 (0.32)
0.31 (0.31)
0.08 (0.08)
0.66 (0.46)
106 ~ 107
105 ~ 106
104 ~ 105
105 ~ 106
106 ~ 107
38 (30)
32 (32)
35 (29)
38 (33)
37 (37)
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OTS
100
OTS
as depo.
100
OTS
ODTS
200
aCalculated with saturated regime. Average values are shown in parentheses.
b
Surface Morphology of Fabricated Thin Films. We next examined atomic force
microscopy (AFM) images of the fabricated thin films in order to determine their surface
morphology, which must be correlated with their FET performance. Figure 4 shows 2 μm ×
2 μm AFM topographic images of 5a-5e-based thin films on SAM-modified Si/SiO2 substrate.
The thin films of 5a and 5e showed relatively large crystalline grains with a bicontinuous
network, which is often observed in high-performance materials. Indeed, the fabricated
OFET devices obtained from 5a and 5e exhibited high mobilities. However, a few dark spots
and clear grain boundaries were also observed in the thin film of 5a, which resulted in its
lower mobility in comparison with 5e. Furthermore, the quality of thin films of 5b and 5c
was poor. The thin film of 5b revealed that these crystallized films had a large root mean
square (RMS) roughness of 8.44 nm, and 5c- and 5d-based thin films showed numerous dark
spots and a discontinuity, defects that lead to a low carrier transport ability.
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Figure 4. AFM height images (2 m  2 m) of the fabricated thin films based on 5a-5e on
SAM-modified Si/SiO2 substrate, which afforded the best device characteristics.
Two-Dimensional Grazing Incidence X-ray Diffraction (2D-GIXD) Patterns of the
Fabricated Thin Films. In order to investigate the molecular orientation in the thin films of
DBADT derivatives 5a-5e, two-dimensional grazing incidence X-ray diffraction (2D-GIXD)
patterns were measured. Figure 5 shows the 2D-GIXD patterns and the corresponding 1D
profiles of 5a-5e thin films on SAM-modified Si/SiO2 substrate. The calculated interlayer
distances are summarized in Table S1. Thin films of 5a exhibited fifth order (00l) diffraction
peaks as spots at the qz direction. The interlayer distance was calculated to be 17.2 Å, which
is consistent with computed longitudinal molecular length. In addition, three characteristic
peaks in the qxy direction were observed as spots, which are often assignable to a herringbone
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structure in the in-plane direction. This indicates that 5a formed a highly ordered 2D layer-
by-layer structure perpendicular to the substrate. It is well known that such a well-ordered
edge-on orientation with herringbone arrangement is suitable for effective 2D carrier
transport in OFET devices,10 and in fact 5a-based OFET devices exhibited high mobilities of
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up to 0.37 cm2 V s . Next, we examined the 2D-GIXD patterns of thin-films of 5b and 5c.
In comparison with 5a and dialkylated DBADTs 5b and 5c, all compounds mainly formed
edge-on orientation in the solid state, indicating no substantial impact of alkyl substitution
and their positions on their main crystalline structures. On the other hand, their crystallinity
and packing structures were different. The thin film based on 5b showed broad (00l)
diffraction peaks and other diffraction peaks (indicated by asterisks) were observed at the qz
direction, indicating the small crystallite size and co-existence of an unsuitable crystallite in
the solid state. The interlayer distance in 5b is shorter than its molecular length calculated
from an optimized geometry, implying that 5b formed an interdigitated structure in each alkyl
layer or a 33° tilted structure relative to the substrate, which may prevent effective
intermolecular electronic coupling. Furthermore, 5b film showed distinct structural disorder
in the in-plane direction, because three diffraction peaks in the qxy direction were observed as
short arcs. Therefore, the mobility of 5b was slightly lower than that of 5a. Thin films of 5c
also showed a fourth order of (00l) diffraction peaks in the qz direction and three short arc-
like peaks in the qxy direction, much like 5b. On the other hand, the calculated d-spacing and
molecular length of 5c are almost the same, indicating that 5c formed a completely edge-on
orientation, which is suitable for high-performance OFETs. However, since 5c formed a poor
surface morphology including the construction of many dark spots and a small grain size, it
exhibited the almost same hole mobility as 5b. In contrast to dialkylated DBADTs 5b and 5c,
diphenyl DBADTs 5d and 5e showed quite different features in the solid state. The interlayer
distances of 5d and 5e were estimated to be 24.7 and 23.7 Å, respectively. Their
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corresponding tilt angles (θ) were almost the same, at 19 and 16°, respectively. Although all
diffraction from 5d film was obtained as spots, it showed fifth order (00l) diffraction patterns
in both qz and qxy directions, indicating that edge-on and face-on orientations coexisted in the
thin films. In general, a face-on orientation is unsuitable for effective carrier transport in
OFET devices, and in fact OFET devices based on 5d showed the relatively low mobility of
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0.08 cm2 V s . Although 5e-based thin films also showed a component of face-on
orientation to some extent, the face-on ratio of 5e was significantly smaller than that of 5d
(vide infra). In addition, 5e film also exhibited intense and spot-like diffraction in all
diffraction patterns, indicating the formation of a highly crystalline and well-ordered structure
in the thin film. Although the reason for the highest hole mobility of 5e is still not
understood at the current stage, a highly ordered crystalline film with the optimal morphology
of 5e may point the way to effective carrier transport in this system. We also reasoned that
the incorporation of two phenyl rings at the optimal positions should enhance the
intermolecular orbital overlap, leading to high hole mobility.
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Figure 5. 2D-GIXD patterns and the corresponding 1D profiles of 5a-5e thin films on a
SAM-treated Si/SiO2 substrate.
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In order to further investigate the molecular orientation quantitatively, we calculated the
face-on ratio of DBADT derivatives 5d and 5e by the pole figure analyses of (001)
diffraction using the 2D-GIXD patterns, as shown in Figure 6.27 The components of face-on
and edge-on orientations were extracted from the integrated areas with pole angle χ ranges of
0-22.5° and 157.5-180° (face-on) and 67.5-112.5 (edge-on), respectively. As a result, the
face-on ratio of 5d was calculated to be 28%, which is considerably higher than that of 5e
(4%). According to these results, installation of phenyl groups can enhance π-orbitals
overlaps, while the ratio of unsuitable face-on crystallites was increased in spite of their
different substitution positions. This tendency of mis-oriented structure is similar as phenyl
substituted BBTBDT and DNTT derivatives.17d,27b Thus, we hypothesized that twisted
phenyl substituents on π-cores may interact with neighboring moieties along the multi-
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direction, resulting in the increased face-on ratio in comparison with parent and dialkylated
derivatives.
According to the 2D-GIXD results of DBADT derivatives, 5c and 5e, which possessed
substituents at 4,12-positions formed more ordered packing structures as well as 5a in
comparison with 5b and 5d. This tendency has not been fully proved, but we presume that
molecular orbitals were quite important (Figure 7). In the HOMO orbitals of 5a, no HOMO
coefficients existed on 4,12-positions, while 3,11-positions were electron rich sites. Hence,
HOMO orbitals of 5c and 5e were similar as 5a, suggesting no significant effect of alkyl and
phenyl substitution on their electronic structures. On the other hand, in 5b and 5d, HOMO
orbitals of outer benzothiophene units were slightly delocalized like a node, which is not
suitable for effective π-orbital overlaps.17d,19 Therefore, we may think that functionalization
of no electron rich sites is highly important for favorable packing motif as well as parent
cores and enhancement of semiconducting properties.
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Figure 6. (a) 2D-GIXD patterns and (b) Pole figure plots extracted from the (001) diffraction
of 5d and 5e thin films.
Figure 7. HOMO orbitals of 5a, 5d, and 5e obtained from DFT calculation.
Conclusion
In summary, we have successfully synthesized an array of DBADT derivatives through
sequential palladium-catalyzed Suzuki-Miyaura or Negishi coupling, epoxidation, and Lewis
acid-catalyzed cycloaromatization without the formation of structural isomers. UV-vis
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absorption spectra showed small differences regardless of the positions of the substituents on
a DBADT framework. In addition, all DBADT derivatives showed almost the same HOMO
energy levels around 5.5 eV, which is enough to ensure high air stability. The fabricated
OFET devices based on DBADT derivatives exhibited typical p-type semiconducting
behavior under ambient conditions in the dark. Specifically, the maximum hole mobility
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reached to 0.66 cm2 V s in 5e-based OFET devices. On the other hand, dialkyl-substituted
DBADT derivatives 5b and 5c showed relatively low mobilities due to the formation of
polymorphs, disordered structure in the in-plane direction, and small crystallite size for 5b,
and also poor film quality for 5c. This indicates that the substitution position effect of
alkylated DBADTs on the OFET performance is small. In sharp contrast, diphenylated
DBADT’s performance depended strongly on their substitution position. Intriguingly, the
molecular orientation could be controlled by the substituents and their positions; diphenyl-
substituted DBADT 5e showed a significantly lower component of face-on orientation (4%)
in comparison with that of 5d (28%), leading to higher hole mobility. We conclude that
installation of functional groups into non-electron-rich sites of the parent core is important for
creating more suitable packing structure in the solid state. To achieve higher mobility as well
as lower voltage operation, we are currently undertaking the design and synthesis of novel
organic materials with extended -electron systems, and incorporating extended or multiple
acene moieties into molecular frameworks.
Experimental Section
General. All reactions were carried out under an argon atmosphere using standard Schlenk
techniques. Glassware was dried in an oven (130 ºC) and heated under reduced pressure
prior to use. Dehydrated tetrahydrofuran (THF), N,N-dimethylformamide (DMF), and
toluene were purchased from Kanto Chemicals Co., Ltd. For thin layer chromatography
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(TLC) analyses throughout this work, Merck precoated TLC plates (silica gel 60 GF254, 0.25
mm) were used. Silica gel column chromatography was carried out using Silica gel 60 N
(spherical, neutral, 40-100 μm) from Kanto Chemicals Co., Ltd. NMR spectra (1H and
13C{1H}) were recorded on Varian INOVA-600 (600 MHz) spectrometer. Chemical shifts
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are in parts per million relative to CDCl3 at 7.26 ppm for H and at 77.0 ppm for C{1H}
NMR spectra. Infrared spectra were recorded on a Shimadzu IRPrestige-21
spectrophotometer and reported in wave numbers (cm–1). HRMS were determined on a
JEOL JMS-700 MStation (double-focusing mass spectrometer). Elemental analyses were
carried out with a Perkin-Elmer 2400 CHN elemental analyzer at Okayama University.
5-Octylbenzo[b]thiophene
(1c),28
6-phenylbenzo[b]thiophene
(1d),16
5-
phenylbenzo[b]thiophene (1e),29 and 2,5-diiodo-1,4-benzendicarboxaldehyde (2)30 were
synthesized according to the reported procedures. All other chemicals were used without
further purification.
Synthesis of 6-Octylbenzo[b]thiophene (1b). To a solution of 1-octene (1.17 mL, 7.5
mmol, 1.5 equiv) in anhydrous THF (100 mL) in a 200 mL 2-neck round-bottomed flask
under argon was added 9-BBN dimer (915 mg, 3.75 mmol, 0.75 equiv) at room temperature.
The reaction mixture was stirred at 60 ºC for 1 h, then allowed to cool to room temperature,
and Pd(dba)2 (144 mg, 0.25 mmol, 5 mol %), [HPt-Bu3]BF4 (145 mg, 0.25 mmol, 10 mol %),
powdered KOH (842 mg, 15 mmol, 6 equiv), and 6-bromobenzo[b]thiophene (1.07 g, 5
mmol, 1 equiv) were added at room temperature. The reaction mixture was stirred at 85 ºC
for 8 h, quenched with water (10 mL), and extracted with chloroform (100 mL × 2). The
combined organic layers were washed with brine and dried over MgSO4. Filtration and
evaporation afforded a pale yellow liquid. Column chromatography on silica gel (eluent:
hexane) gave the titled product 1b (1.20 g, 4.85 mmol, 97%) as a colorless liquid. Rf = 0.56
1
(hexane). FT-IR (KBr, cm ): 3101 (s), 3073 (s), 3051 (s), 3022 (s), 2953 (w), 2924 (w),
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2853 (w), 1464 (m), 1396 (m), 1202 (s), 881 (m), 816 (m), 785 (s), 721 (m). H NMR (600
MHz, CDCl3, rt): δ 0.88 (t, J = 7.2 Hz, 3H), 1.25-1.38 (m, 10H), 1.67 (quintet, J = 7.2 Hz,
2H), 2.73 (t, J = 7.2 Hz, 2H), 7.19 (dd, J = 8.4, 1.6 Hz, 1H), 7.28 (dd, J = 5.4, 0.6 Hz, 1H),
7.35 (d, J = 5.4 Hz, 1H), 7.68 (d, J = 0.6 Hz, 1H), 7.73 (d, J = 8.4 Hz, 1H). 13C{1H} NMR
(150 MHz, CDCl3, rt): δ 14.3, 22.8, 29.41, 29.47, 29.6, 31.9, 32.0, 36.2, 121.8, 123.3, 123.7,
125.3, 125.5, 137.7, 139.5, 140.1. Anal. Calcd for C16H22S: C, 77.99; H, 9.00%. Found: C,
77.64; H, 9.31%.
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Synthesis of 2,5-Bis(benzo[b]thiophene-2-yl)-1,4-phthalaldehyde (3a). To a solution of
2 (386 mg, 2.2 mmol, 1 equiv) in anhydrous THF (30 mL) in a 50 mL Schlenk tube under
argon were added 2-benzothienylboronic acid (392 mg, 2.2 mmol, 2.2 equiv), Pd(dba)2 (29
mg, 0.05 mmol, 5 mol %), Sphos (41 mg, 0.1 mmol, 10 mol %), potassium fluoride (267 mg,
4.6 mmol, 4.6 equiv), and H2O (110 μL, 6 mmol, 6 equiv) at room temperature. The reaction
mixture was stirred at reflux for 4 h, quenched with water (10 mL) and poured into MeOH
(100 mL), producing a yellow precipitate, which was filtered, and dried under vacuum to
afford the titled product 3a (381 mg, 0.96 mmol, 96%) as a yellow solid. Mp = 264-266 ºC.
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FT-IR (KBr, cm ): 3096 (s), 3059 (w), 3048 (w), 3028 (w), 2891 (s), 1684 (w), 1531 (m),
1375 (m), 1152 (m), 908 (m), 862 (m), 810 (m), 737 (m), 721 (m). 1H NMR (600 MHz,
CDCl3, rt): δ 7.38 (s, 2H), 7.44-7.46 (m, 4H), 7.87 (d, J = 6.6 Hz, 2H), 7.92 (d, J = 6.0 Hz,
2H), 8.28 (s, 2H), 10.35 (s, 2H). 13C{1H} NMR (CDCl
, 150 MHz, rt): δ 122.3, 124.2, 125.2,
3
125.5, 127.1, 131.1, 137.3, 137.5, 139.9, 140.9, 190.9. Anal. Calcd for C24H14O2S2: C, 72.34;
H, 3.54%. Found: C, 72.16; H, 3.29.
A Typical Procedure for 3: Synthesis of 2,5-Bis(6-octylbenzo[b]thiophen-2-yl)-1,4-
phthalaldehyde (3b). To a solution of 6-octylbenzo[b]thiophene (1b) (542 mg, 2.2 mmol,
2.2 equiv) in anhydrous THF (20 mL) in a 50 mL Schlenk tube under an argon atmosphere
was added n-butyllithium (1.6 M in hexane, 1.5 mL, 2.4 mmol, 2.4 equiv) at 78 ºC. After
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being stirred for 1 h at room temperature, the mixture was cooled to 0 ºC, then zinc chloride
(327 mg, 2.4 mmol, 2.4 equiv) was added to the reaction mixture, which was allowed to
warm to room temperature, and stirred for 1 h. 2,5-Diiodo-1,4-benzendicarboxaldehyde (2)
(386 mg, 1 mmol, 1 equiv), Pd(dba)2 (29 mg, 0.05 mmol, 5 mol %), and tris(2-
furyl)phosphine (23 mg, 0.01 mmol, 10 mol %) were added at room temperature. The
resulting reaction mixture was stirred at reflux for 3 h, quenched with water (10 mL), and
then poured into MeOH (100 mL), producing a yellow precipitate, which was filtered, then
dried under vacuum to afford the titled product 3b (551 mg, 0.88 mmol, 88%) as a yellow
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solid. Mp = 121-122 ºC. FT-IR (KBr, cm ): 3049 (s), 2955 (m), 2924 (w), 2853 (m), 1686
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(w), 1468 (s), 1369 (m), 1150 (m), 907 (s), 847 (m), 795 (s), 721 (s). H NMR (600 MHz,
CDCl3, rt): δ 0.89 (t, J = 7.2 Hz, 6H), 1.26-1.39 (m, 20H), 1.70 (quintet, J = 7.8 Hz, 4H), 2.77
(t, J = 7.8 Hz, 4H), 7.28 (dd, J = 7.8, 1.2 Hz, 2H), 7.31 (s, 2H), 7.70 (s, 2H), 7.76 (d, J = 8.4
Hz, 2H), 8.26 (s, 2H), 10.34 (s, 2H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 14.1, 22.7,
29.26, 29.31, 29.5, 31.7, 31.9, 36.1, 121.4, 123.8, 126.3, 126.9, 131.0, 136.2, 137.0, 137.5,
137.9, 140.9, 141.2, 191.0. Anal. Calcd for C40H46O2S2: C, 77.12; H, 7.44%. Found: C,
76.90; H, 7.40%.
Dialdehydes 3c-3e were synthesized according to the same procedure as 3b.
2,5-Bis(5-octylbenzo[b]thiophen-2-yl)-1,4-phthalaldehyde (3c). Yellow solid. 96% yield
1
(894 mg, 1.44 mmol). Mp = 115-117 ºC. FT-IR (KBr, cm ): 2957 (m), 2922 (w), 2852 (m),
1686 (w), 1528 (m), 1458 (s), 1364 (m), 1252 (s), 962 (s), 887 (m), 816 (m), 723 (s). 1H
NMR (600 MHz, CDCl3, rt): δ 0.89 (t, J = 7.2 Hz, 6H), 1.26-1.38 (m, 20H), 1.69 (quintet, J =
7.8 Hz, 4H), 2.76 (t, J = 7.8 Hz, 4H), 7.28 (d, J = 8.4, 1.2 Hz, 2H), 7.31 (s, 2H), 7.67 (s, 2H),
7.80 (d, J = 8.4 Hz, 2H), 8.26 (s, 2H), 10.34 (s, 2H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ
14.1, 22.7, 29.26, 29.29, 29.5, 31.8, 31.9, 35.9, 121.9, 123.4, 126.7, 126.9, 130.9, 137.0,
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137.3, 137.6, 138.3, 140.16, 140.22, 191.0. Anal. Calcd for C40H46O2S2: C, 77.12; H, 7.44%.
Found: C, 77.10; H, 7.44%.
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2,5-Bis(6-phenylbenzo[b]thiophen-2-yl)-1,4-phthalaldehyde (3d). Yellow solid. 98% yield
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(540 mg, 0.98 mmol). Mp > 270 ºC. FT-IR (KBr, cm ): 3099 (s), 3080 (s), 3059 (s), 3024
(s), 2851 (m), 1636 (w), 1528 (m), 1476 (m), 1369 (w), 1298 (m), 1159 (m), 854 (w), 818 (w),
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758 (w), 698 (m). H NMR (600 MHz, CDCl3, rt): δ 7.41 (t, J = 7.8 Hz, 4H), 7.50 (t, J = 7.8
Hz, 4H), 7.69-7.71 (m, 6H), 7.93 (d, J = 8.4 Hz, 2H), 8.12 (s, 2H), 8.31 (s, 2H), 10.34 (s, 2H).
13C{1H} NMR (150 MHz, CDCl3, rt) was not obtained due to poor solubility. Anal. Calcd
for C36H22O2S2: C, 78.52; H, 4.03%. Found: C, 78.28; H, 4.03%.
2,5-Bis(5-phenylbenzo[b]thiophen-2-yl)-1,4-phthalaldehyde (3e). Yellow solid. Quant (825
1
mg, 1.50 mmol). Mp > 270 ºC. FT-IR (KBr, cm ): 3078 (s), 3051 (s), 3030 (s), 2862 (s),
1
1683 (w), 1447 (m), 1362 (m), 1287 (m), 1150 (m), 901 (m), 820 (m), 758 (w), 689 (m). H
NMR (600 MHz, CDCl3, rt): δ 7.40 (t, J = 7.8 Hz, 2H), 7.44 (s, 2H), 7.50 (t, J = 7.8 Hz, 4H),
7.68-7.69 (m, 4H), 7.70 (d, J = 1.8 Hz, 2H), 7.98 (d, J = 8.4 Hz, 2H), 8.07 (d, J = 1.8 Hz, 2H),
8.32 (s, 2H), 10.38 (s, 2H). 13C{1H} NMR (150 MHz, CDCl3, rt) was not obtained due to
poor solubility. Anal. Calcd for C36H22O2S2: C, 78.52; H, 4.03%. Found: C, 78.17; H, 3.86%.
A Typical Procedure for 4: Synthesis of 2,2’-(2,5-Bis(benzo[b]thiophen-2-yl)-1,4-
phenylene)bis(oxirane) (4a). To a solution of 3a (40 mg, 0.1 mmol, 1 equiv) in anhydrous
acetonitrile (3 mL) in a 20 mL Schlenk tube under an argon atmosphere, were added
trimethylsulfonium iodide (49 mg, 0.24 mmol, 2.4 equiv) and powdered KOH (31 mg, 0.55
mmol, 5.5 equiv) at room temperature. The reaction mixture was vigorously stirred at 60 ºC
for 3 h, quenched with water (5 mL), and extracted with chloroform (30 mL × 2). The
combined organic layers were washed with brine, then dried over MgSO4. Filtration and
evaporation afforded the titled product 4a (41.7 mg, 0.098 mmol, 98%) as a pale yellow solid.
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(m), 1157 (m), 880 (m), 862 (w), 833 (m), 750 (w), 727 (w). H NMR (600 MHz, CDCl3, rt):
δ 2.86 (dd, J = 5.7, 2.4 Hz, 1H), 2.91 (dd, J = 5.7, 2.4 Hz, 1H), 3.22 (t, J = 6.0 Hz, 2H), 4.18
(dd, J = 3.9, 2.4 Hz, 2H), 7.37-7.42 (m, 6H), 7.57 (s, 2H), 7.83-7.88 (m, 4H). 13C{1H} NMR
(150 MHz, CDCl3, rt): δ 50.82, (50.85), 51.7, (51.9), 122.3, 123.9, 124.20, 124.24, 124.8,
126.7, 134.3, 135.7, 140.1, 140.4, 140.8. Chemical shifts assigned to one of two
diastereomers are shown in parentheses. HRMS (EI+) m/z: [M]+ Calcd for C26H18O2S2:
426.0748. Found: 426.0748.
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Diepoxides 4b-4d were synthesized according to the same procedure as 4a.
2,2’-(2,5-Bis(6-octylbenzo[b]thiophen-2-yl)-1,4-phenylene)bis(oxirane) (4b). Pale yellow
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solid. Quant (326 mg, 0.50 mmol). Mp = 91-93 ºC. FT-IR (KBr, cm ): 2955 (w), 2926 (w),
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2853 (w), 1560 (w), 1406 (m), 1200 (s), 1146 (s), 883 (m), 808 (m), 727 (s). H NMR (600
MHz, CDCl3, rt): δ 0.88 (t, J = 7.2 Hz, 6H), 1.26-1.39 (m, 20H), 1.68 (quintet, J = 7.8 Hz,
4H), 2.74 (t, J = 7.2 Hz, 4H), 2.85 (dd, J = 3.0, 2.4 Hz, 1H), 2.94 (dd, J = 3.0, 3.0 Hz, 1H),
3.20-3.22 (m, 2H), 4.17 (dd, J = 2.4, 1.2 Hz, 2H), 7.22 (dd, J = 1.2, 6.6 Hz, 2H), 7.35 (s,
2H), 7.55 (d, J = 2.4 Hz, 2H), 7.63 (s, 2H), 7.76 (d, J = 7.8 Hz, 2H). 13C{1H} NMR (150
MHz, CDCl3, rt): δ 14.2, 22.6, 29.3, 29.4, 29.6, 31.9, 32.0, 36.0, 50.5, 51.5, (51.6), 121.5,
123.1, 123.9, 125.8, (126.5), 126.7, 134.2, 135.7, 137.7, 139.8, 140.7, 141.0. Chemical shifts
assigned to one of two diastereomers are shown in parentheses. HRMS (EI+) m/z: [M]+ Calcd
for C42H50O2S2: 650.3252. Found: 650.3222.
2,2’-(2,5-Bis(5-octylbenzo[b]thiophen-2-yl)-1,4-phenylene)bis(oxirane) (4c). Pale yellow
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solid. 86% yield (279 mg, 0.43 mmol). Mp = 87-88 ºC. FT-IR (KBr, cm ): 2955 (w), 2926
(w), 2853 (w), 1560 (m), 1465 (m), 1406 (m), 1250 (s), 1159 (s), 883 (m), 808 (m), 727 (s).
1H NMR (600 MHz, CDCl3, rt): δ 0.89 (t, J = 6.9 Hz, 6H), 1.27-1.35 (m, 20H), 1.69 (quintet,
J = 7.5 Hz, 4H), 2.74 (t, J = 6.9 Hz, 4H), 2.85 (dd, J = 5.6, 2.4 Hz, 1H), 2.91 (dd, J = 6.3, 2.7
Hz, 1H), 3.20-3.23 (m, 2H), 4.18 (dd, J = 3.1, 2.7 Hz, 2H), 7.22 (dd, J = 8.1, 1.5 Hz, 2H),
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7.36 (s, 2H), 7.56 (d, J = 2.4 Hz, 2H), 7.63 (s, 2H), 7.77 (d, J = 8.4 Hz, 2H). 13C{1H} NMR
(150 MHz, CDCl3, rt): δ 14.4, 22.9, 29.5, 29.6, 29.8, 32.0, 32.1, 36.2, 51.0, 51.8, (52.0),
122.6, 123.4, 124.1, 126.1, 127.0, 134.5, 135.7, 137.9, 139.9, 140.6, 141.0. Chemical shifts
assigned to one of two diastereomers are shown in parentheses. HRMS (EI+) m/z: [M]+ Calcd
for C42H50O2S2: 650.3252. Found: 650.3223.
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2,2’-(2,5-Bis(6-phenylbenzo[b]thiophen-2-yl)-1,4-phenylene)bis(oxirane) (4d). Pale yellow
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solid. 90% yield (443 mg, 0.77 mmol). Mp = 237-238 ºC. FT-IR (KBr, cm ): 3053 (s),
3028 (s), 2988 (s), 2918 (s), 1462 (m), 1373 (m), 1298 (s), 1250 (s), 1163 (s), 955 (m), 851
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(m), 760 (w), 729 (m). H NMR (600 MHz, CDCl3, rt): δ 2.89 (dd, J = 5.4, 3 Hz, 1H), 2.94
(dd, J = 5.4, 3 Hz, 1H), 3.24-3.26 (m 2H), 4.21 (t, J = 3 Hz, 2H), 7.39 (t, J = 7.2 Hz, 2H),
7.45 (s, 2H), 7.49 (t, J = 7.2 Hz, 4H), 7.61 (d, J = 1.8 Hz, 2H), 7.66 (dd, J = 8.4, 1.2 Hz, 2H),
7.69 (d, J = 7.8 Hz, 4H), 7.89 (d, J = 8.4 Hz, 2H) 8.08 (s, 2H). 13C{1H} NMR (150 MHz,
CDCl3, rt): δ 50.7, (50.8), 51.6, (51.7), 120.4, 123.79, (123.83), 124.0, 124.4, 126.7, 126.9,
127.37, (127.39), 128.9, 134.2, 134.3, 135.57, (135.58), 138.1, 139.2, 140.9, (141.01), 141.03,
(141.1). Chemical shifts assigned to one of two diastereomers are shown in parentheses.
HRMS (EI+) m/z: [M]+ Calcd for C38H26O2S2: 578.1374. Found: 578.1363.
Synthesis of 2,2’-(2,5-Bis(5-phenylbenzo[b]thiophen-2-yl)-1,4-phenylene)bis(oxirane)
(4e). To a solution of 3e (441 mg, 0.68 mmol, 1 equiv) in benzonitrile (30 mL) in a 50 mL
Schlenk tube under an argon atmosphere, were added trimethylsulfonium iodide (333 mg,
1.63 mmol, 2.4 equiv) and powdered KOH (210 mg, 3.80 mmol, 5.5 equiv) at room
temperature. The reaction mixture was vigorously stirred at 60 ºC for 3 h, quenched with
water (5 mL), and extracted with chloroform (30 mL × 2). The combined organic layers were
washed with brine and dried over MgSO4. Filtration and evaporation afforded the titled
product 4e (278 mg, 0.48 mmol, 71%) as a pale yellow solid. Mp = 220-222 ºC. FT-IR (KBr,
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cm ): 3082 (s), 3053 (m), 3032 (m), 2995 (m), 2911 (s), 1501 (m), 1445 (w), 1373 (m), 1244
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(m), 1157 (m), 870 (w), 818 (m), 758 (w), 725 (m). H NMR (600 MHz, CDCl3, rt): δ 2.89
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(dd, J = 5.4, 1.5 Hz, 1H), 2.94 (dd, J = 5.4, 1.5 Hz, 1H), 3.24-3.26 (m 2H), 4.21 (dd, J = 3.6,
1.2 Hz, 2H), 7.39 (t, J = 7.2 Hz, 2H), 7.48-7.51 (m, 6H), 7.61 (d, J = 2.4 Hz, 2H), 7.63 (dd, J
= 8.4, 1.8 Hz, 2H), 7.69 (d, J = 7.2 Hz, 4H), 7.93 (d, J = 8.4 Hz, 2H) 8.04 (d, J = 1.2 Hz, 2H).
13C{1H} NMR (150 MHz, CDCl3, rt): δ 50.70, (50.73), 51.6, (51.7), 122.1, 122.4, 124.27,
(124.31), 124.4, 126.7, 126.9, 127.3, (127.4), 128.9, 134.2, (134.3), 135.61, (135.63), 138.2,
139.3, 140.60, (140.61), 141.1, 141.41, (141.45). Chemical shifts assigned to one of two
diastereomers are shown in parentheses. HRMS (EI+) m/z: [M]+ Calcd for C38H26O2S2:
578.1374. Found: 578.1374.
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A Typical Procedure for 5: Synthesis of Dibenzo[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-
b’]dithiophene (5a). To a solution of 4a (116 mg, 0.27 mmol, 1 equiv) in anhydrous 1,2-
dichloroethane (10 mL) in a 50 mL Schlenk tube under an argon atmosphere, was added
indium chloride (12 mg, 0.054 mmol, 20 mol %) at room temperature. The reaction mixture
was stirred at reflux for 48 h, quenched with water (10 mL), and then poured into MeOH
(100 mL) and filtered. The filter cake was rinsed successively with water (50 mL), hexane
(50 mL), acetone (50 mL), and hot chloroform (50 mL). Drying in vacuo afforded the titled
product 5a as a pale yellow solid, which was further purified by sublimation to give
analytically pure samples (82 mg, 0.21 mmol, 78%) as a yellow solid. Mp > 270 ºC. FT-IR
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(KBr, cm ): 3051 (s), 3015 (s), 1527 (s), 1429 (m), 1085 (m), 878 (w), 809 (m), 770 (w), 735
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(w), 689 (m). H NMR (600 MHz, CDCl3, rt) was not obtained due to poor solubility; nor
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was C{1H} NMR (CDCl3, 150 MHz, rt). Anal. Calcd for C26H14S2: C, 79.96; H, 3.61%.
Found: C, 79.90; H, 3.35%.
DBADT derivatives 5b-5e were synthesized according to the same procedure as 5a.
3,11-Dioctyldibenzo[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-b’]dithiophene (5b).
Yellow solid.
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84% yield (75 mg, 0.12 mmol). Mp > 270 ºC. FT-IR (KBr, cm ): 2957 (m), 2922 (w), 2872
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(m), 2851 (w), 1466 (s), 1414 (s), 1257 (s), 878 (m), 806 (m), 721 (s), 691 (s). H NMR (600
MHz, CDCl3, rt) was not obtained due to poor solubility; nor was 13C{1H} NMR (150 MHz,
CDCl3, rt). Anal. Calcd for C42H46S2: C, 82.03; H, 7.54%. Found: C, 81.93; H, 7.54%
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4,12-Dioctyldibenzo[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-b’]dithiophene (5c).
Yellow solid.
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78% yield (170 mg, 0.27 mmol). Mp = 265 ºC. FT-IR (KBr, cm ): 3049 (s), 3034 (s), 3009
(s), 2956 (m), 2922 (w), 2872 (m), 2852 (w), 1541 (s), 1456 (m), 1252 (s), 988 (s), 878 (w),
806 (m), 723 (s), 623 (s). 1H NMR (600 MHz, CDCl3, rt) was not obtained due to poor
solubility; nor was 13C{1H} NMR (150 MHz, CDCl3, rt). Anal. Calcd for C46H54S2: C, 82.33;
H, 8.11%. Found: C, 82.19; H, 8.11%.
3,11-Diphenyldibenzo[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-b’]dithiophene (5d). Yellow solid.
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90% yield (97 mg, 0.18 mmol). Mp > 270 ºC. FT-IR (KBr, cm ): 3057 (s), 3030 (s), 3005
(s), 1541 (s), 1466 (m), 1412 (m), 1244 (s), 1078 (s), 880 (w), 808 (w), 768 (m), 754 (w), 696
(m). 1H NMR (600 MHz, CDCl3, rt) was not obtained due to poor solubility; nor was
13C{1H} NMR (150 MHz, CDCl3, rt). Anal. Calcd for C38H22S2: C, 84.10; H, 4.09%. Found:
C, 83.97; H, 3.91%.
4,12-Diphenyldibenzo[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-b’]dithiophene (5e). Yellow solid.
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91% yield (103 mg, 0.19 mmol). Mp > 270 ºC. FT-IR (KBr, cm ): 3049 (s), 3030 (w), 3005
(m), 1541 (s), 1452 (m), 1250 (m), 1093 (s), 874 (w), 820 (m), 802 (m), 758 (w), 700 (m),
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638 (m). H NMR (600 MHz, CDCl3, rt) was not obtained due to poor solubility; nor was
13C{1H} NMR (150 MHz, CDCl3, rt). Anal. Calcd for C38H22S2: C, 84.10; H, 4.09%. Found:
C, 84.18; H, 3.76%.
Instrumentation and Theoretical Calculations. UV-vis absorption spectra were measured
using a Shimadzu UV-2450 UV-vis spectrometer. Cyclic voltammograms (CVs) were
recorded on Electrochemical Analyzer CHI-600B in acetonitrile containing
tetrabutylammonium hexafluorophosphate (TBAP, 0.1 M) as supporting electrolyte at a scan
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rate of 100 mV/s. A Pt electrode (surface area: A = 0.071 cm2, BAS), a Ag/Ag+ (Ag wire in
0.01 M AgNO3/0.1 M TBAP/CH2Cl2), and a Pt wire electrode were used as working,
reference, and counter electrodes, respectively. Dynamic force-mode atomic force
microscopy was carried out using an SPA 400-DFM (SII Nano Technologies). Two-
dimensional grazing incidence X-ray diffraction (2D-GIXD) analyses were carried out at
SPring-8 on beamlines BL46XU. The samples were irradiated at a fixed angle on the order
of 0.12° through a Huber diffractometer with an X-ray energy of 12.39 keV (λ = 1 Å), and
the GIXD patterns were recorded on a 2D image detector (Pilatus 300K). DFT calculations
were performed at the B3LYP/6-31G(d) level using the Gaussian 09, Revision A.02 program
package.31
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Fabrication of Vapor Deposited OFET Devices. Typical bottom-gate top-contact OFET
devices were fabricated as follows. All processes except for substrate cleaning were
performed under a nitrogen atmosphere. A heavily doped n-Si wafer with 200 nm thick
thermally grown SiO2 (Ci = 17.3 nF cm−2) as the dielectric layer was used as the substrate.
The Si/SiO2 substrates were carefully cleaned using ultrasonication with acetone and
isopropanol for 10 min, respectively. After being dried, the substrates were irradiated by UV-
O3 for 20 min, and then treated with the solution of 0.1 M n-octyltrichlorosilane (OTS), n-
octadecyltrichlorosilane (ODTS) in anhydrous toluene to form a self-assembled monolayer
(SAM). The active layers were deposited on the treated substrate by vapor deposition at the
rate of 0.1 Å/s. Thermal annealing was performed at 100, 150, and 200 °C for 30 min on a
hotplate in a glove box. After treatment, gold electrodes (50 nm thick) were deposited
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through a shadow mask on the top of the active layer under reduced pressure (5  10 Pa).
The current-voltage characteristics of the OFET devices were measured at room temperature
in air on a Keithley 6430 Sub-Femtoamp Remote Sourcemeter combined with a Keithley
2400 SourceMeter Unit. Field-effect mobilities were calculated in the saturation regime of
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the ID using following equation,
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ID = (WCi/2L) μ (VG-Vth)2
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Where Ci is the capacitance of the SiO2 insulator. ID is the source-drain current, and VD, VG,
and Vth are the source-drain, gate, and threshold voltages, respectively. Current on/off ratio
(Ion/off) was determined from a minimum ID at around VG = 60 V.
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ASSOCIATED CONTENT
Supporting Information. The Supporting Information is available free of charge on the
ACS Publications website at DOI:. 1H and 13C NMR spectra are available for all new
compounds, as well as details of physicochemical properties, computational data, surface
morphologies, and device characteristics.
AUTHOR INFORMATION
Corresponding Author
* E-mail: ynishiha@okayama-u.ac.jp
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENTS
This work was partly supported by ACT-C, JST Grant Number JPMJCR12YW, Japan, and a
Grant-in-Aid for Scientific Research (KAKENHI) (No.15J07968) from JSPS. The 2D-GIXD
measurements were performed at BL46XU of SPring-8 with the approval of the Japan
Synchrotron Radiation Research Institute (JASRI) (Proposal 2016A1542, 2016A1768,
2016B1875). The authors gratefully thank Prof. Itaru Osaka (Hiroshima University) and Dr.
Tomoyuki Koganezawa (JASRI) for providing the 2D-GIXD images, Profs. Koichi Mitsudo
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and Seiji Suga (Okayama University) for the measurement of CV, Prof. Naoshi Ikeda
(Okayama University) for providing the AFM images, and Ms. M. Kosaka and Mr. M.
Kobayashi at the Department of Instrumental Analysis, Advanced Science Research Center,
Okayama University, for the elemental analyses. The help of the SC-NMR Laboratory of
Okayama University in obtaining the NMR spectral measurements is gratefully
acknowledged.
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