21

ターフェニレン化合物の合成及び溶液プロセスに適応可能なＴＦＴ用ターフェニレン半導体材料
渡大山辺橋本真知敏人一秀Synthesis of Terphenylene Compounds and Solution Processable Terphenylene
Semiconductors for TFT
Makoto WATANABE
Tomokazu OHASHI
Toshihide YAMAMOTO

The linear terphenylene (benzo[3,4]cyclobuta[1,2-b]biphenylene) compounds were synthesized fromtetrabromoterphenyls with lithiation followed by a four membered ring formation reaction using cupric chloride
for the first time. Since the tetrabromoterphenyls were prepared by a palladium−catalyzed coupling reaction, thissynthetic method can provide a wide range of symmetric and unsymmetric terphenylene compounds with highrigidity. It is known that the molecular structure of the unsubstituted terphenylene was almost planar and thearrangement of molecules was classified as a herringbone packing such as pentacene. TFTs were fabricated in
top −contact configuration on the HMDS−treated Si／SiO2 substrate by vacuum deposition. Terphenylene
compounds were purified by recrystallization, used as semiconductors, and we have found for the first time thatthey had p−channel field effect properties. Dibenzoterphenylene and naphthoterphenylene (TC1), which is an
isomer of dibenzoterphenylene, exhibited mobilities of 0.0058 and 6.0 × 10−4 cm2／V・s in air, respectively.
Introducing substituents to TC1 developed soluble TC2 and TC3. The performance of devices using TC2 and TC3
were highly improved to give mobilities of 0.022 and 0.055 cm 2／V・s in air, respectively. Since a device ofpentacene had a mobility of 0.033 cm2／V・s in air in the same conditions of fabrication, TC2 and TC3 havecomparable performance to pentacene in air. TFT devices using TC2 and TC3 were also prepared by solution
process and showed mobilities of 1.3 × 10−4 and 2.9 × 10−3 cm2／V・s, respectively, without detailed investigationof coating conditions.

Especially, the bis(ethynyl) substituted acenes were１．Introduction

reported to afford high performance for solution

The most important material properties for theprocess１）. Although the possibility of photooxidation oforganic semiconductors in TFTs are high mobility,

the highly conjugated molecules such as acenes cannot

stability, and processability. The stability of transistors

be excluded２）, fused ring compounds with long axes

and semiconductors in solution process under ambientare expected to give high performance by increased

conditions has become increasingly important forπ−stacking. From the point of view, we focused on thepractical applications. The organic semiconductors withlinear terphenylene compounds, which have not beenhigh performance reported to date are shown in Fig. 1.

used as organic electronic materials.

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TOSOH Research ＆ Technology Review Vol.51（2007）

SS

S

S

SSS

S

i-Pr
i-Pr
i-Pr
SiSS

S
i-Pr Si i-Pr
i-Pr

SFig. １

Organic semiconductors with high performance

We report here the synthesis of terphenylene(TC1), which is an isomer of 2, were synthesizedcompounds, the device fabrication, and the FET(Fig. 2). In addition, the easily soluble TC2 and TC3,

characteristics.

which are alkyl substituted TC1s, were also obtained.
These terphenylene compounds were purified byrecrystallization. Especially, TC2 and TC3 have good

２．Synthesis of Terphenylenessolubility of 0.24 and 0.80 wt％ in toluene at 100℃,

The linear terphenylene (benzo[3,4]cyclobuta[1,2−b]biphenylene) (1) is a known compound３）

and adopts

respectively, and were recrystallized from toluene toyield orange small crystals.

４）. Since the literature s

The UV−vis absorption spectra of vacuum−deposited

synthetic method was only limited to unsubstituted andfilms of TC1 and TC2 are shown in Fig. 3. Whilesilyl substituted types, we explored the new synthetic

absorption peaks appeared almost at the samea herringbone structureroute for the more fused types and found that
tetrabromoterphenyls underwent lithiation followed byoxidative ring formation reaction using cupric chloride togive the terphenylenes. Since the tetrabromoterphenyls
1were prepared by a palladium−catalyzed coupling2reaction, this methodology can provide a wide range of
fused symmetric and unsymmetric terphenylene
TC1compounds with high rigidity (Scheme1).
Dibenzoterphenylene (2) and naphthoterphenylene

Fig. ２Terphenylene compounds

Br2eq.

IBrBrI

B（OH）2, Pd（PPh3）4

Br

BrToluene, EtOH, H2O，Na2CO3
Br1）BuLi, THF
2）CuCl2

Scheme １

New synthetic method of terphenylenes（ 22 ）

Br

東ソー研究・技術報告 第51巻（2007）

1.2

Table １

Field − effect mobility and on ／ off ratio forterphenylene compounds in air

Absorbance［nom.］

1.0

compound
2TC1
TC2
TC3
pentacene

0.80.6TC1

0.4

23mobility（cm2 ／ V・s） on ／ off ratio
0.0058
5.3 × 103
6.0 × 10 − 4
1.0 × 103
0.022
2.4 × 106
0.055
7.1 × 106
0.033
6.6 × 102

temperature. All the organic FET devices using the0.2
TC2

terphenylene compounds showed p −channel FET
0400

500

600

700

characteristics except for 1５）. Field−effect mobilities

800

Wavelength［nm］

Fig. ３

were calculated from the saturation regime and current

UV − vis spectra of TC1 and TC2 in thin film

on/off ratios were determined from the IDS between VG＝ 0 V and −40 V. The FET performances of vacuum−

wavelengths, the spectrum of TC2 gave a clearer

deposited films are summarized in Table１. With little

waveform indicating the thin film of TC2 has less

optimization the mobility of dibenzoterphenylene (2)scattering than that of TC1 and the longest absorption

was found to be 0.0058 cm 2 /V・s. There were noat 498 nm. Since the UV−vis absorption spectrum ofdifferences between atmospheres measured regarding

TC2 in tetrahydrofuran solution showed its longest

electrical properties of the device of 2. On the otherabsorption peak at 489 nm, the 9 nm red shift washand, while the device of TC1 showed an enhanced

observed from solution to a thin film. And the opticalmobility (0.019 cm2/V・s) by one order of magnitude

band gap of 2.36 eV was estimated from the absorption

in vacuum, the mobility highly decreased in air (6.0 ×edge of the spectrum of the thin film. In pentacene, the10−4 cm2/V・s).

band gap from the absorption edge around 1.8 eV.

When TC2 was used as an active layer, the mobility

Therefore, the band gap of TC2 is significantly higher

was increased by two orders of magnitude (0.022

than that of pentacene, indicating higher redox

cm2/V・s) in air compared to that of TC1. In addition,stability.

the on/off ratio was also drastically improved from 1.0
×103 to 2.4 ×106. In the case of TC3, which is anotheralkylated TC1 and has a higher solubility than TC2, the３．Field−Effect Transistors

device exhibited the mobility as high as 0.055 cm2／V・s and the on／off ratio of 7.1 × 106. The device with a［1］Device Fabrication
The field effect transistors were fabricated in top−＋vacuum deposition film of pentacene was prepared

contact configuration on a heavily doped n −Si wafer

under the same fabrication conditions as above and thewith a thermally grown oxide layer (200 nm). On theelectrical properties were evaluated in air giving a hole

top of the organic thin film, gold drain and source

mobility of 0.033 cm2/V・s and an on/off ratio of 6.6 ×electrodes were deposited to yield devices with a

10 2 . Since the mobilities and the on/off ratios bychannel length of 15 μm and a channel width of 500 μmeasurement of the devices using TC2 and TC3 in

m. A thin film (50 nm) of terphenylenes as an active

vacuum were the same as or only slightly higher thanlayer was vacuum−deposited on the HMDS−treatedthose in air, it is emphasized that the high performance

Si/SiO 2 substrate at room temperature. The TFTof TC2 and TC3, which mobilities are comparable todevices using TC2 and TC3 were also prepared bypentacene, is maintained in air. Fig. 4 demonstrates thesolution deposition (spin−coating and drop−casting) ofFET characteristics of the device of TC2.
A FET device using TC2 from solution was also

the 0.1 wt％ solution (100 or 90 ℃) in toluene on theSi／SiO2 substrate.

prepared and its electrical properties were calculated. A［2］Electrical Characteristics

0.1 wt ％ solution of TC2 in hot toluene was spin coatedAll measurements were performed in air at room

onto the Si/SiO2 substrate at room temperature. The（ 23 ）

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TOSOH Research ＆ Technology Review Vol.51（2007）

drop−casting. A solution of TC3 in toluene at 90℃ was

8.0

Drain Current［−μA］

Vg ＝− 50V
7.0

applied onto the Si／SiO 2 substrate at 90℃ and the

6.0

solvent was left to evaporate. The mobility wasincreased by one order of magnitude (2.9 × 10−3 cm2／5.0− 40V
4.0V・s) compared to that of TC2 and the on／off ratio

3.0(1.5 × 104) was comparable to TC2.

2.0− 30V

1.0− 20V− 10/0V0010203040
Drain Voltage［− V］

４．Conclusions

50

The new highly fused terphenylene compounds such

1010−610−73.5
VDS＝−50V
3.0in vacuumin vacuum

2.5210 − 8μ＝0.023 cm ／Vs
Vt＝9.8V

2.0

10 − 91.5

10 − 10in air

10 − 11in air

1.0
2μ＝0.022 cm ／Vs
Vt＝13.5V

10 − 120.5

10 − 130Fig.４

10203040Gate Voltage［− V］

50method with cupric chloride and the organic FETDrain Current@Vd ＝− 50V1 ／ 2［103A1 ／2］

Drain Current［A］

as 2 and TCl−3 were synthesized by the coupling−5devices using these terphenylenes as an active layer
were fabricated. We found that the devices using theseterphenylene compounds exhibited p−type transistor
responses for the first time. Especially, the devices
using TC2 and TC3 gave not only comparable
mobilities to that of pentacene but also high current
on/off ratios even in air. Therefore, fused terphenylene
compounds are thought to have the same potential of0

electrical properties as pentacene and the much higher
stability. Although the mobilities in solution process
have not been high enough yet, alkylated TCls (TC2FET characteristics of devices withvacuum−deposited films of TC2and TC3) have high solubility in toluene and gave thedevices bearing a FET activity. We will continue to3.0

Drain Current［A］

102.5

−92.0
10 − 10μ＝ 1.3 × 10 − 4cm2 ／Vs
1.5

10 − 111.0

10 − 120.5

10 − 13

examine the optimization of the structure ofDrain Current@Vd ＝− 50V1 ／ 2［104A1 ／ 2］

Vd ＝− 10，− 20，− 30，− 40，− 50V

10 − 8terphenylene compounds that is utilized for practicalprinting process.

５．Experimental［1］General procedure for synthesis oftetrabromoterphenyl
A nitrogen 100 ml schlenk flask was charged with

Id@Vd ＝− 50V1 ／ 210 − 14− 101,4−dibromo−2,5−diiodobenzene (4.39 g, 9.00 mmol),

00102030Gate Voltage［− V］

4050tetrakis(triphenylphosphine)palladium (974 mg, 0.84mmol), 2−bromophenylboronic acid (Aldrich, 4.16 g,Fig. ５

Transfer characteristics of a device with asolution − deposited film of TC220.7 mmol), toluene (72 ml), ethanol (18 ml), and an
aqueous solution (22 ml) of sodium carbonate (5.72 g,solvent was then left to evaporate at room temperature.
−4A field−effect mobility of 1.3 × 10 and an on/off ratio
454.0 mmol) under nitrogen. The mixture was stirred at85 ℃ for 15 h. After cooling to room temperature,of 4.6×10 were obtained without detailed investigation

dichloromethane and brine were added, and theof the device fabrication conditions. Fig. 5 shows theorganic layer was separated and concentrated underFET characteristics of the device obtained by thereduced pressure. The residue was recrystallized fromsolution method using TC2.

toluene to give 4.18 g (85％ y) of white needle crystals

In the case of TC3, a FET activity was obtained byof 2,2 ,5 ,2 −tetrabromo−1,1 ,4 −1 −terphenyl.

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東ソー研究・技術報告 第51巻（2007）［2］General procedure for synthesis of25

７． References

terphenylene
A nitrogen 100 ml schlenk flask was charged with１）M. M. Payne, S. R. Parkin, J. E. Anthony, C. −C.

2,2 ,5 ,2 −tetrabromo−1,1 ,4 −1 −terphenyl (269 mg,Kuo, T. N. Jackson, OFET from solution−deposited

0.492 mmol) prepared above and tetrahydrofuran (23functionalized acenes. J. Am. Chem. Soc ., 127,ml) under nitrogen. After cooling to −80 ℃, sec−

4986−4987 (2005).

butyllithium (cyclohexane solution of 0.98M) (5.0 ml,２ ） K. Ono et al., Photooxidation of pentacene

4.9 mmol) was added. The mixture was stirred for 20

derivatives. Tetrahedron, 63, 9699−9704 (2007).

min and copper (II) chloride (828 mg, 6.20 mmol) was３）K. P. C. Vollhardt et al., Synthesis of terphenylene

added at −75 ℃. The mixture was gradually warmed to(1). J. Am. Chem. Soc., 107, 5670−5687 (1985).

room temperature. After brine and toluene were added,４）A. Schleifenbaum, N. Feeder, K. P. C. Vollhardt,

the resulting organic layer was separated, washed with

X−ray crystal structure of terphenylene (1).

brine, and concentrated under reduced pressure. The

Tetrahedron Lett., 42, 7329−7332 (2001).

residue was washed with hexane and recrystallized５）The compound 1 showed no FET characteristics.

from toluene to give 24.0 mg (22％ y) of red crystals(plates) of terphenylene.

６．Acknowledgement
The authors gratefully thank Dr. Toshihide Kamataand Dr. Satoshi Hoshino of National Institute ofAdvanced Industrial Science and Technology for the
fabrication of FET devices and the measurement of theelectrical characteristics.

著

者

氏名 渡 辺 真 人
Makoto WATANABE著

者

氏名 大 橋 知 一

著

者

氏名 山 本 敏 秀

Tomokazu OHASHI

Toshihide YAMAMOTO

入社 昭和60年 4 月 1 日

入社 平成15年 4 月 1 日

入社 平成 2 年 4 月 1 日

所属 四日市研究所

所属 四日市研究所

所属 四日市研究所

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