Trialkylsilylethynyl-substituted triphenylenes and hexabenzocoronenes: Highly soluble liquid crystalline materials and their hole transport abilities

Article abstract of DOI:10.1016/j.tet.2015.05.071

Four triphenylene (TP) and four hexa-peri-hexabenzocoronene (HBC) derivatives with trialkylsilylethynyl groups were prepared and characterized by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. All compounds were highly soluble in less-polar organic solvents and exhibited a columnar phase, Col_h or Col_r for the TPs, and Col_h for the HBCs. The hole transport ability in the HBCs' columnar phase, 0.4-1.5×10^-3 cm² V^-1 s^-1 at 40-180°C, and its temperature dependence were determined by the time-of-flight method using a solution technique.

Full text of DOI:10.1016/j.tet.2015.05.071

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Accepted Manuscript
Trialkylsilylethynyl-substituted triphenylenes and hexabenzocoronenes: highly soluble
liquid crystalline materials and their hole transport abilities
Takuji Hirose, Yutaro Miyazaki, Mizuki Watabe, Sho Akimoto, Tatsuya Tachikawa,
Koichi Kodama, Mikio Yasutake
PII:
S0040-4020(15)00762-0
10.1016/j.tet.2015.05.071
TET 26789
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 13 April 2015
Revised Date: 19 May 2015
Accepted Date: 20 May 2015
Please cite this article as: Hirose T, Miyazaki Y, Watabe M, Akimoto S, Tachikawa T, Kodama K,
Yasutake M, Trialkylsilylethynyl-substituted triphenylenes and hexabenzocoronenes: highly soluble liquid
crystalline materials and their hole transport abilities, Tetrahedron (2015), doi: 10.1016/j.tet.2015.05.071.
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Trialkylsilylethynyl-substituted
triphenylenes and hexabenzocoronenes:
Highly soluble liquid crystalline materials
and hole transport abilities
Takuji Hirose,* Yutaro Miyazaki,
Mizuki Watabe, Sho Akimoto,
Tatsuya Tachikawa, Koichi Kodama,
Mikio Yasutake
1

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ACCEPTED MANUSCRIPT
Trialkylsilylethynylꢀsubstituted triphenylenes and hexabenzocoronenes:
highly soluble liquid crystalline materials and their hole transport abilities
Takuji Hirose,a, Yutaro Miyazaki,a Mizuki Watabe,a Sho Akimoto,a Tatsuya Tachikawa,a Koichi
*
Kodama,a and Mikio Yasutakeb
a
Graduate School of Science and Engineering, Saitama University, 255 ShimoꢀOkubo, Sakuraꢀku,
Saitama 338ꢀ8570, Japan.
b
Comprehensive Analysis Center for Science, Saitama University, 255 ShimoꢀOkubo, Sakuraꢀku,
Saitama 338ꢀ8570, Japan.
Corresponding author. Eꢀmail address: thirose@mail.saitamaꢀu.ac.jp (T. Hirose).
Keywords: trialkylsilylethynyl group, triphenylene, hexaꢀperiꢀhexabenzocoronene, liquid crystal, hole
transport ability
ABSTRACT
Four triphenylene (TP) and four hexaꢀperiꢀhexabenzocoronene (HBC) derivatives with
trialkylsilylethynyl groups were prepared and characterized by differential scanning calorimetry,
polarizing optical microscopy, and Xꢀray diffraction measurements. All compounds were highly soluble
in lessꢀpolar organic solvents and exhibited a columnar phase, Colh or Colr for the TPs, and Colh for the
HBCs. The hole transport ability in the HBCs’ columnar phase, 0.4−1.5 × 10-3 cm2 V-1 s-1 at 40−180 °C, and
its temperature dependence were determined by the timeꢀofꢀflight method using a solution technique.
2

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1. Introduction
The development of new organic semiconductors is currently a challenging project,1 and interest in
liquid crystals (LCs) has grown significantly for application to electronic devices such as solar cells,
organic lightꢀemitting diodes, and organic fieldꢀeffect transistors.2 Semiconducting organic molecules
and materials, including liquid crystalline ones, cannot yet compete with their inorganic counterparts in
terms of charge transport ability and industrial performance. However, they have important
advantages: versatile synthetic processes, lower production costs, and compatibility with other
materials such as flexible polymeric films and inorganic substrates.
To increase the charge transport ability of LCs, aromatic structures are expected to be a key factor in
improving the performance owing to their high πꢀelectron density. For a columnar LC phase, the
introduction of a highly symmetric polyaromatic hydrocarbon structure is typically an important
strategy and leads to high oneꢀdimensional charge transport like that through a wire. However, at the
same time, it is generally recognized that the LC transition temperature rises and the solubility
decreases as the fused aromatic core size is enlarged.3 As a result, low solubility hinders the
processability, detailed study, and even efficient syntheses.
We have synthesized and studied several types of discotic liquid crystals, including their conductive
properties.4 During this work, we have used pyrene as a core structure to lower the crystalline−LC
phase transition temperature and improve the solubility. In the previous work, we have shown that the
introduction of trialkylsilyl groups in a conjugated system is effective not only to raise the conductivity
but also to increase the solubility in common organic solvents.4c If it is applicable to other systems, large
and highly symmetric aromatic structures can be introduced into LCs, and high charge transport ability
is expected owing to their larger π–π interaction or overlap. In this study, eight new discotic liquid
crystals were synthesized using triphenylene (TP), a typical core of columnar LC compounds, and
hexaꢀperiꢀhexabenzocoronene (HBC), one of the largest aromatics, having trialkylsilyl groups as a
terminal of the side chains, and their chemical and physical properties, including the hole transport
ability, were investigated.
2. Results and discussion
2.1.
Design and Syntheses of Triphenylene [TPSi(
[HBCSi( )] Derivatives
m,n)] and Hexaꢀperiꢀhexabenzocoronene
m
Four TP derivatives, TPSi(
derivatives, HBCSi( ) ( = 10, 12, 14, and 16), were designed by attaching trialkylsilylethynyl groups
at each periphery. For TPSi( ), to enlarge the πꢀconjugation, a phenylethynyl moiety was introduced
between the TP core and the terminal group. On the other hand, six trialkylsilylethynyl groups were
m,n) (m = 8, 9, 10; n = 1, 8, 9, 10) and four hexaꢀperiꢀhexabenzocoronene
m
m
m,n
directly attached to the HBC core. The final steps of TPSi(m,n) and HBCSi(m) syntheses are shown in
3