Oxygen- and sulfur-bridged bianthracene V-shaped organic semiconductors

Article abstract of DOI:10.1246/bcsj.20170030

Highly π-electron conjugated backbones are of great interest for applications to organic electronic devices, e.g., organic field-effect transistors and organic photovoltaics. A series of oxygen- and sulfur-bridged bianthracene V-shaped π-electronic cores are facilely synthesized. Both V-shaped molecules possess bent structures induced by the intermolecular interaction in a herringbone-packing manner. A theoretical calculation study reveals that the driving force of the bent structures originates from the strong dispersion energy. Also, the bent conformation plays a vital role in the formation of a dense packing structure, resulting in an attractive intermolecular overlap. An examination of the charge transport demonstrates that the hole mobility is up to 2.0 sq cm/Vs. Sulfur-bridged V-shaped π-electronic cores are more suitable for two-dimensional carrier-transport than oxygen-bridged analogs.

Full text of DOI:10.1246/bcsj.20170030

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Advance Publication Cover Page
Oxygen- and Sulfur-Bridged Bianthracene V-Shaped Organic Semiconductors
Chikahiko Mitsui, Masakazu Yamagishi, Ryoji Shikata, Hiroyuki Ishii, Takeshi Matsushita,
Katsumasa Nakahara, Masafumi Yano, Hiroyasu Sato, Akihito Yamano,
Jun Takeya, and Toshihiro Okamoto*
Advance Publication on the web May 16, 2017
doi:10.1246/bcsj.20170030
© 2017 The Chemical Society of Japan

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Oxygen- and Sulfur-bridged Bianthracene V-shaped Organic Semiconductors
Chikahiko Mitsui,1 Masakazu Yamagishi,1 Ryoji Shikata,2 Hiroyuki Ishii,3,7 Takeshi Matsushita,4 Katsumasa
Nakahara,5 Masafumi Yano,2 Hiroyasu Sato,6 Akihito Yamano,6 Jun Takeya,1,5 and Toshihiro Okamoto*1,5,7
1Department of Advanced Materials Science, Graduate School of Frontier Sciences, The Univ. of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba 277-8561, Japan.
2Chemistry, Materials and Bioengineering Major, Graduate School of Science and Engineering, Kansai Univ., 3-3-35, Yamate-cho, Suita,
Osaka 564-8680, Japan.
3Institute of Applied Physics and Tsukuba Research Center for Interdisciplinary Materials Science, Univ. of Tsukuba, 1-1-1 Tennodai,
Tsukuba, Ibaraki 305-8573, Japan.
4JNC Petrochemical Corp., 5–1 Goikaigan, Ichihara, Chiba 290–8551, Japan.
5The Institute of Scientific and Industrial Research (ISIR), Osaka Univ., 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
6Rigaku Corp., 3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666, Japan.
7PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
E-mail: tokamoto@k.u-tokyo.ac.jp
Abstract
A series of oxygen- and sulfur-bridged bianthracene
dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT),4 and
their alkyl-substituted derivatives.5 These materials exhibit
excellent carrier mobilities, which are superior to that of
currently used amorphous silicon. BTBT and DNTT have
thieno[3,2-b]thiophene substructures corresponding to benzo-
and dibenzo[b,k]chrysene isostructures.6 These substructures
are not acene-type but phenacene-type electronic structures.
Notably, these thienoacenes exhibit a higher air stability than
other linear acenes with the same number of the aromatic rings,
such as tetracene and hexacene due to the lower-lying levels of
the highest occupied molecular orbitals (HOMOs) as well as
the elimination of the reactive position such as the central
6,13-positions of pentacene.7 Since the successful introduction
of the thieno[3,2-b]thiophene substructure into a π-electronic
backbone was achieved, many other research groups have
V-shaped π-electronic cores are facilely synthesized. We
clarify their fundamental properties and aggregated structures
in single crystals as well as measure their transistor
performances in single crystal field-effect transistors. Both
V-shaped molecules possess bent structures induced by the
intermolecular interaction in a herringbone-packing manner. A
theoretical calculation study reveals that the driving force of the
bent structures originates from the strong dispersion energy.
Additionally, the bent conformation plays a crucial role in the
formation of a dense packing structure, resulting in an
attractive intermolecular overlap. An examination of the charge
transport indicates that the hole mobility is up to 2.0 cm2/Vs.
Finally, to understand the anisotropies of the mobility in single
crystals, the transistors are evaluated when the channel
direction is either parallel or orthogonal to the column direction
in the herringbone packing along with their band structure
calculations. Sulfur-bridged V-shaped π-electronic cores are
more suitable for two-dimensional carrier-transport than
oxygen-bridged analogs.
started
to
develop
extensively
thieno[3,2-b]thiophene-containing derivatives and evaluate
their charge-transport properties.4-5, 8
Recently, we developed V-shaped π-electronic cores
(π-cores),
dinaphtho[2,3-b:2',3'-d]furan
(DNF–V)
and
-thiophene (DNT–V) (See Fig. 1a), which are composed of
oxygen- and sulfur-bridged binaphthalene.9 DNF–V and
DNT–V have unique structural features with respect to their
single-crystal structures. Unexpectedly, their molecular
1. Introduction
structures are not planar; instead, they exhibit a bent
Highly π-electron conjugated backbones are of great
interest for applications to organic electronic devices; namely,
organic field-effect transistors (OFETs)1 and organic
photovoltaics (OPVs).2 In the case of OFETs, the π-electron
system composed of benzene and heterole rings plays an
important role in advancing research. Recently Takimiya et al.
conformation in a herringbone packing manner with dihedral
angles between the two naphthalene rings of 4.08° for DNF–V
and 13.88° for DNT–V (Fig. 1a). Meanwhile their theoretical
optimization on a single molecule results in a completely flat
conformation.
We also evaluated their carrier transporting abilities with
single crystal transistors. They exhibit high mobilities up to 1.1
cm2/Vs for DNF–V and 1.5 cm2/Vs for DNT–V, and their
mobilities can be further improved by finely controlling the
developed
easy-to-handle organic semiconducting materials, namely,
[1]benzothieno[3,2-b][1]benzothiophene
(BTBT),3
a
series of tremendously promising and

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aggregation form because these π-cores, assuming
b)ꢀ
herringbone-packing structures, stack with
a
slight
displacement in the molecular longitudinal axis. We introduced
long alkyl side chains on the appropriate positions of their
π-cores so that alkylated DNF–V and DNT–V form
herringbone packing without displacement and exhibit hole
mobilities as high as 1.3 and 9.5 cm2/Vs in solution-grown
single-crystal transistors, respectively.9 Thus, V-shaped π-cores
are promising candidates for solution processable organic
semiconductors. Their FETs with binaphthalene species,
however, exhibit non-negligible threshold voltages due to their
deep HOMO levels. Such findings of DNF–V and DNT–V
motivated us to elucidate the nature of a series of V-shaped
π-cores and further investigate the extended V-shaped π-cores
(Fig. 1a), namely dianthra[2,3-b:2’,3’-d]furan (DAF–V) and
dianthra[2,3-b:2’3’-d]thiophene (DAT–V).10
Oꢀ
Sꢀ
Oꢀ
Sꢀ
–5.0ꢀ
140ꢀ
–5.08ꢀ
–5.15ꢀ
138ꢀ
–5.2ꢀ
–5.4ꢀ
–5.6ꢀ
–5.8ꢀ
120ꢀ
100ꢀ
80ꢀ
114ꢀ
–5.56ꢀ
–5.41ꢀ
99ꢀ
89ꢀ
The molecular designs of DAF–V and DAT–V present
several expected advantages (Fig. 1b). 1) Based on theoretical
calculations, the relatively small reorganization energies under
hole transport (λh) are estimated to be 89 meV for DAF–V and
99 meV for DAT–V, which are smaller than those of DNF–V
(114 meV), DNT–V (138 meV),11 and DNTT (130 meV).
These relatively small reorganization energies suggest that
bianthracene-fused congeners have a high potential as carrier
transporting materials. 2) The HOMO energy levels are higher
than those of naphthalene fused analogs due to the π-electron
extension. 3) The variable orbital coefficient of the HOMO is
on the bridging group 16 element. 4) Similar to the case of
reported DNT–V and DNF–V, the molecular shape should
influence the aggregated structure in the solid state, depending
on the bridging elements and π-conjugated length.
Figure 1. a) Chemical structures and molecular structures in
single crystals of DNT–V and DNF–V, and the chemical
structures of DAF–V and DAT–V in this work. b) Calculated
reorganization energies of holes, λh (blue squares) and HOMO
levels of V-shaped derivatives with HOMO configurations
calculated at the B3LYP/6-31G(d) level.
2. Experimental
2.1. Materials: Reagents and Starting Materials
BBr3 and N,N-dimethylcarbamoyl chloride were
purchased from Tokyo Chemical Industry Co. Fe(acac)3 was
purchased from Sigma–Aldrich. 1,1,2,2-Tetrachloroethane and
o-dichlorobenzene (oDCB) were purchased from Wako Pure
Chemical Industries. n-BuLi, triethylamine, pyridine, and all
anhydrous solvents were purchased from Kanto Chemical Co.
DMF was distilled prior to use. Zeolite HSZ-360 was
purchased from the Tosoh Corporation. 2-Methoxyanthracene
was synthesized according to a modified procedure from the
literature.12
Herein we report a study on the chemistry and material
science of oxygen- and sulfur-bridged bianthracene V-shaped
π-cores compared with binaphthalene analogs. To understand
the potential utilities of V-shaped π-cores as active
semiconducting materials, we describe the synthetic method
and their fundamental properties, single-crystal structures,
theoretical calculations, and charge transporting capabilities
evaluated by single crystal transistors.
a)ꢀ
2.2. Methods: Typical Synthesis and Characterization
O
All reactions were carried out under
a nitrogen
DNF–Vꢀ
O
atmosphere. Air- or moisture-sensitive liquids and solutions
were transferred via a syringe or a Teflon cannula. Analytical
thin-layer chromatography (TLC) was performed on glass
plates with a 0.25-mm 230–400 mesh silica gel containing a
fluorescent indicator (Merck Silica gel 60 F254). TLC plates
were checked under exposure to an ultraviolet lamp (254 nm
and 365 nm) and visualized by dipping into 10%
phosphomolybdic acid in ethanol and subsequent heating on a
hot plate. Flash-column chromatography was performed on
Kanto silica gel 60. Open-column chromatography was
performed on Wakogel C-200 (75–150 µm). All NMR spectra
were recorded on JEOL ECA600 or JEOL ECS400
spectrometer. The chemical shifts are reported in parts per
million (ppm, δ scale) from the residual protons in deuterated
DAF–Vꢀ
4.08°ꢀ
Extended
π-coreꢀ
S
S
DNT–Vꢀ
DAT–Vꢀ
13.88°ꢀ
“Bent” Conformationꢀ
1
solvent for H NMR (δ 7.26 ppm for chloroform, δ 5.93 ppm
for 1,1,2,2-tetrachloroethane, and δ 2.04 ppm for acetone) and
from the solvent carbon for 13C NMR (e.g., δ 77.16 ppm for
chloroform, δ 74.00 ppm for 1,1,2,2-tetrachloroethane, and δ
29.80 ppm for acetone). The data are presented in the following
format: chemical shift, multiplicity (s = singlet, d = doublet, t =
triplet, m = multiplet), coupling constant in Hertz (Hz), signal
area integration in natural numbers, and assignment (in italics).
Mass spectra were measured on a JEOL JMS-T100LC

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APCI/ESI mass spectrometer. Melting points and elemental
analyses were collected on a Mettler Toledo MP70 Melting
Point System and on a J-Science Lab JM10 MICRO CORDER,
respectively.
2.3. Methods: Typical Fundamental Properties and
Structural Analyses
UV-vis absorption was measured on a JASCO V-570
spectrophotometer. Photoluminescence was measured using a
Hitachi F-4500 fluorescence spectrophotometer. The TG–DTA
measurement was carried out with a Rigaku Thermo Plus EVO
II TG 8120 apparatus. Photoelectron yield spectroscopy
(PYS)13 was performed on a Sumitomo Heavy Industries
Advanced Machinery PYS-202 apparatus. The XRD data for
the single crystal of DAF–V and DAT–V were collected on
Rigaku R-AXIS RAPID II and R-AXIS 191-R imaging plate
diffractometers with CuKα radiation, respectively. FET
removing the solvent in the mother liquor, the crude material
was purified by silica gel column chromatography
(hexane:THF = 70:30) to afford the desired compound (844 mg,
0.23 mmol, additional 9%). Yield: 96%. M.p.: 279–280 °C.
1H NMR (600 MHz, acetone-d6): δ 7.43–7.52 (m, 4H, ArH),
7.54 (s, 2H, ArH), 8.04 (d, J = 9.2 Hz, 2H, ArH), 8.07 (d, J =
8.8 Hz, 2H, ArH), 8.18 (s, 2H, ArH), 8.38 (s, 2H, ArH), 8.57 (s,
2H, ArH), 8.81 (s, 2H, OH). 13C NMR (150 MHz, acetone-d6):
δ 108.9, 123.9, 125.1, 126.3, 127.2, 128.5, 129.1, 129.2, 131.4,
131.8, 132.0, 133.3, 134.0, 154.3. TOF HRMS (APCI): Calcd
for C28H19O2 [M+H] 387.1385, found, 387.1378.
Synthesis of Dianthra[2,3-b:2',3'-d]furan (DAF–V)
To a yellow suspension of 2,2'-bianthracene-3,3'-diol
(1.55 g, 4.00 mmol) in 80 mL of oDCB was added 465 mg of
Zeolite HSZ-360 and the reaction mixture was stirred at 160 °C
for 20 h. After the reaction mixture was cooled to room
temperature, the resulting yellow precipitate was collected by
filtration. The collected material was purified by vacuum
sublimation to afford the desired compound (1.14 g, 3.09 mmol,
77%) as a yellow solid. M.p.: N.A. 1H NMR (600 MHz,
CDCl2CDCl2, 120 °C): δ 7.44–7.49 (m, 4H, ArH), 7.92 (s, 2H,
ArH), 8.00 (d, J = 8.4 Hz, 2H, ArH), 8.04 (d, J = 8.4 Hz, 2H,
ArH), 8.49 (s, 2H, ArH), 8.62 (s, 2H, ArH), 8.66 (s, 2H, ArH).
The 13C NMR spectrum could not be recorded due to the low
solubility. TOF HRMS (APCI): Calcd for C28H17O [M+H]
369.1279, found, 369.1264. Anal. Calcd for C28H16O: C, 91.28;
H, 4.38. Found C, 91.34; H, 4.53.
characteristics were measured using
semiconductor parameter analyzer.
2.4. Synthetic procedure
a
Keithley 4200
Synthesis of 2-Methoxyanthracene (1)
To
a suspension of 2-methoxyanthracene-9,10-dione
(2.38 g, 10.0 mmol) in 200 mL of i-PrOH was added NaBH4
(2.27 g, 60.0 mmol, 6.0 mol amt.). The mixture was gradually
heated to the reflux temperature and maintained for 24 h.
(Caution: gas evolves during the reaction) After cooling to 0 °C
in ice water, the mixture was carefully hydrolyzed with a 1 N
hydrochloric acid aqueous solution, and the resulting yellow
precipitate was collected by filtration. After dissolving the
collected yellow solid by chloroform, the crude material was
purified by a short pad of a silica gel column employing
chloroform to afford the desired compound (1.32 g, 6.33 mmol,
Synthesis
of
O,
O'-[2,2'-Bianthracene]-3,3'-diyl
bis(dimethylcarbamothioate) (4)
To a yellow suspension of 2,2'-bianthracene-3,3'-diol (483
mg, 1.25 mmol) in THF (7.5 mL) were added triethylamine
(0.39 mL), pyridine (10.0 mL), and N,N-dimethylcarbamothioic
chloride (402 mg, 3.25 mmol, 2.6 mol amt.). The resulting
yellow suspension was heated at 65 °C for 20 h. After
removing the solvent in vacuo, the crude material was purified
by silica gel column chromatography (hexane:ethylacetate =
80:20) to afford the desired compound (430 mg, 0.767 mmol,
1
63%) as a pale-yellow solid. H NMR (600 MHz, CDCl3): δ
3.97 (s, 3H, OCH3), 7.16 (d, J = 8.4 Hz 1H, ArH), 7.21 (s, 1H,
ArH), 7.40–7.46 (m, 2H, ArH), 7.90 (d, J = 8.4 Hz, 1H, ArH),
7.95, (d, J = 8.4 Hz, 1H, ArH), 7.97 (d, J = 8.4 Hz, ArH), 8.28
(s. 1H, ArH), 8.35 (s, 1H, ArH). The spectral data of this
compound were identical to those reported previously.14
1
Synthesis of 3,3'-Dimethoxy-2,2'-bianthracene (2)
61%) as a pale-yellow solid. Mp.: 233–234 °C. H NMR (600
To a solution of 2-methoxyanthracene (3.00 g, 14.4
mmol) in THF (51 mL) was added 1.60 M n-BuLi in hexane
(9.9 mL, 15.8 mmol, 1.1 mol amt.) at 0 °C. After stirring at
0 °C for 1 h, Fe(acac)3 (5.58 g, 15.8 mmol, 1.1 mol amt.) was
added at 0 °C. The resultant mixture was stirred at room
temperature for 10 h. After the reaction was finished, the
resulting red precipitate was collected by filtration. The crude
material was purified by silica gel column chromatography
(hexane:chloroform = 60:40) to afford a pale-yellow solid (1.54
MHz, CDCl3): δ 3.01 (s, 6H, NCH3), 3.11 (s, 6H, NCH3),
7.47–7.51 (m, 4H, ArH), 7.81 (s, 2H, ArH), 8.01–8.03 (m, 4H,
ArH), 8.19 (s, 2H, ArH), 8.46 (s, 2H, ArH), 8.47 (s, 2H, ArH).
13C NMR (150 MHz, CDCl3): δ 38.5, 43.2, 120.4, 125.6, 126.0,
126.1, 126.9, 128.1, 128.5, 129.8, 130.6, 131.2, 131.8, 131.9,
132.3, 149.8, 187.4. TOF HRMS (APCI): Calcd for
C34H29N2O2S2 [M+H] 561.1670, found, 561.1855.
Synthesis of Dianthra[2,3-b:2',3'-d]thiophene (DAT–V)
O,
O'-[2,2'-Bianthracene]-3,3'-diyl
1
g, 3.72 mmol, 52%). M.p.: 239–240 °C. H NMR (600 MHz,
bis(dimethylcarbamothioate) (561 mg, 1.0 mmol) was heated in
a sealed Pyrex tube at 300 °C for 8 h. The reaction mixture was
cooled to ambient temperature. The crude material was purified
by vacuum sublimation to afford the desired compound (261
CDCl3): δ 3.94, (s, 6H, OCH3), 7.32 (s, 2H, ArH), 7.41 (dd, J =
7.8 Hz, 7.8 Hz, 2H, ArH), 7.46 (dd, J = 7.8Hz, 7.8 Hz, 2H,
ArH), 7.94–7.99 (m, 6H, ArH), 8.34 (s, 2H, ArH), 8.39 (s, 2H,
ArH). 13C NMR (150 MHz, CDCl3): δ 55.8, 103.6, 124.0,
124.5, 125.6, 126.4, 127.8, 128.3, 128.4, 130.5, 130.6, 131.4,
132.3, 132.8, 156.3. TOF HRMS (APCI): Calcd for C30H23O2
[M+H] 415.1698, found, 415.1707.
1
mg, 0.68 mmol, 68%) as an orange solid. M.p.: N.A. H NMR
(600 MHz, CDCl2CDCl2, 120 °C): δ 7.44–7.48 (m, 4H, ArH),
7.99–8.06 (m, 4H, ArH), 8.27 (s, 2H, ArH), 8.42 (s, 2H, ArH),
8.63 (s, 2H, ArH), 8.84 (s, 2H, ArH). The 13C NMR spectrum
could not be recorded due to low solubility. TOF HRMS
(APCI): Calcd for C28H17S [M+H] 385.1051, found, 385.1044.
Anal. Calcd for C28H16S: C, 87.47; H, 4.19. Found C, 87.33; H,
4.38.
Synthesis of 2,2'-Bianthracene-3,3'-diol (3)
To
a
yellow
suspension
of
3,3'-dimethoxy-2,2'-bianthracene (1.04 g, 2.51 mmol) in
dichloromethane (10 mL) was added 1.0 M BBr3 (7.5 mL, 7.5
mmol, 3.0 mol amt.) in dichloromethane at 0 °C. The resulting
mixture was stirred at room temperature for 5 h. After the crude
material was poured into iced water, the organic layer was
extracted with THF and EtOAc, and then dried over MgSO4.
The solvent was subsequently removed to ~20 mL in vacuo,
and acetone was added to afford a yellow solid (844 mg, 2.18
mmol, 87%), which was collected by vacuum filtration. After
2.5. Fabrication of single-crystal transistors and FET
measurements
Single crystals of semiconducting materials were grown
by a physical vapor transport (PVT) technique.15 As the active
layers, the crystals were laminated on SiO2 (500 nm)/doped Si
substrates, and the surfaces, which were preliminarily treated
with heptadecafluorodecyltrimethoxysilane, self-assembled a