Fluoro-substituted Phenyleneethynylenes: Acetylenic n-Type Organic Semiconductors
Daisuke Matsuo,
1
Xin Yang,
1
Akiko Hamada,
2
Kyo Morimoto,
2
Takuji Kato,
2
Masayuki Yahiro,
2
Chihaya Adachi,*
2
Akihiro Orita,*
1
and Junzo Otera*
1
1
Department of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005
2
Center for Organic Photonics and Electronics Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395
(Received October 4, 2010; CL-100848; E-mail: orita@high.ous.ac.jp, otera@high.ous.ac.jp)
Fluoro-substituted phenyleneethynylenes are synthesized by
Sonogashira coupling and acetylide-nucleophilic substitution of
fluorobenzenes. Fluoro-substitution of benzenes enables deep
LUMO potential, and CF
3
-substitution provides high electron
mobility in deposited film(® = 5.5 © 10
¹2
cm
2
V
¹1
s
¹1
).
A number of organic materialswith highly expanded ³
systems have been developed for organic field-effect transistors
1
(OFET) and organic light-emitting diodes
2
(OLED). Fluoro-
and fluoroalkyl-substituted arenes have attracted great attention,
because they have low-energy LUMO and may serve as
electron-transporting materials.
3
Although a number of n-type
OFET devices have been fabricated by using electron-trans-
porting materials,
4
carrier mobilities observed in the devices are
insufficient for practical use, and further development of
organic semiconducting material with high mobility is still
necessary. We have been involved in synthesisof phenylene-
ethynylene derivatives
5
and succeeded in application of CF
3
-
substituted phenyleneethynylene 1 (Figure 1) to n-type organic
semiconductor material by invoking the carrier-transporting
properties of phenyleneethynylene array and electron-with-
drawing effect of CF
3
groups.
6
We envisioned that fluoro-
substituted phenyleneethynylenes could serve more efficiently
as n-type semiconductors, because fluorines on benzenes would
give rise to deep HOMO and LUMO levels. We present herein
synthesisof 29, their cyclic voltammograms and preliminary
results of OFET properties using 9 as n-type semiconducting
material.
In Scheme 1 are shown representative synthetic processes
for 4, 6, and 9.
7,8
Decafluorodiphenylethyne (10) was prepared
in 55% yield by coupling between 11 and 12 in the presence of
5 mol% of palladium catalyst and a stoichiometric amount of
copper(I) chloride. The target compound 4 was synthesized in
60% yield by substitution at 4- and 4¤-positions of 10 with
lithium phenylethynide. Similar substitution at the 4-position of
10 with lithium ethynide which was prepared by lithiation of 13
afforded nonafluoro-derivative 6 in 65% yield. In this substitu-
tion reaction, a large excess of 10 was required in order to
suppress formation of bis-adduct, and when only two equiv-
alents of 10 was used, the yieldof 6 decreased to 18%. Terminal
ethyne 13 was provided by Sonogashira coupling between
trimethylsilylethyne and 14, followed by removal of the TMS
group, which had been obtained by one-shot doubleelimination
between benzyl sulfone 15 and iodobenzaldehyde (16). Iodina-
tion of 17 with I
2
/K
3
PO
4
gave an iodide 18 in 55% yield, and
Sonogashira coupling of 18 with trimethylsilylethyne provides
an inseparablemixture of the desired product 19 and trimethyl-
silylethyne-homocoupling product 20 in 86% and 7% yield,
respectively. Treatment of a THF solution of 19 (containing 20)
and 10 with tetrabutylammonium fluoride afforded 9 in 27%
yield.
In order to assess the electroniceffect offluorine on HOMO
and LUMO potentials, cyclic voltammograms of 29 were
recorded in THF by using Ag/AgNO
3
as a reference electrode,
and the half-wave reduction potentials E
red
for 29 are summa-
rized in Table 1.
8,9
Fluoro-substituted phenyleneethynylenes
39 undergo reversibleelectrochemical reduction at ¹1.20 to
¹2.02 V, while 2 does not. It is observed that reduction potential
R
1
R
1
F3C
R
1
R
1
R
1
R
1
R
1
R
1
R
2
R
2
R
2
R
2
R
1
= R
2
= H (1)
R
1
= R
2
= F (9)
CF3
R
2
R
2
R
2
R
2
R
1
R
1
R
1
R
1
R
1
R
2
R
2
R
2
R
2
R
3
R
3
R
3
R
3
R
1
= R
2
= R
3
= R
4
= H (2)
R
1
= F, R
2
= R
3
= R
4
= H (3)
R
2
= R
3
= F, R
1
= R
4
= H (4)
R
1
= R
4
= F, R
2
= R
3
= H (5)
R
1
= R
2
= F, R
3
= R
4
= H (6)
R
1
= R
2
= R
3
= F, R
4
= H (7)
R
1
= R
2
= R
3
= R
4
= F (8)
R
4
R
4
R
4
R
4
R
4
Figure 1. Structures of 19.
[Pd(PPh
3
)
4
] (5 mol%)
CuCl (1.2 equiv)
DMF, i -Pr2NH,
80 °C/ 15 h
I TMS +
12 (1.2 equiv)
F F
F
F F
F F
F
F F
F F F F
F
F F
F
F F
10 55%
TBAF (10 mol%)
THF,
0 °C - rt, 12 h
+ 19 9 27%
11
6 65%
Li
THF,
0 °C - rt, 12 h
10 (3.0 equiv)
TMS
TMS
THF, MeOH,
rt, 4 h
I OHC
SO
2
Ph
ClP(O)(OEt)2
+ I
THF, 0 °C - rt, 6 h
LiHMDS(5.0 equiv)
[Pd(PPh
3
)
4
], CuI
toluene, i -Pr
2
NH,
60 °C, 15 h
K
2
CO
3
82%
13 96%
14
15
16
13/BuLi
10 4 60%
Li
THF,
-78 °C - rt, 15 h
F F
F F
DMF,
130 °C, 2 h
F F
F F
I F
3
C F
3
C
I
2
, K
3
PO
4 [Pd(PPh
3
)
4
], CuI
toluene, i -Pr
2
NH,
80 °C, 20 h
TMS (1.2 equiv) F F
F F
F
3
C TMS
18 55%
19 86%
17
TMS TMS
20 7%
10
Scheme 1. Synthetic processes for 4, 6, and 9.
Published on the web November 11, 2010 1300
doi:10.1246/cl.2010.1300
© 2010 The Chemical Society of Japan Chem. Lett. 2010, 39, 13001302 www.csj.jp/journals/chem-lett/