Published on the web June 15, 2010
771
Synthesis and Crystal Structures of 1,4,8,11-Tetraalkyl-6,13-diphenylpentacenes
Chitoshi Kitamura,*1 Takao Naito,1 Akio Yoneda,1 Takeshi Kawase,1 and Toshiki Komatsu2
1Department of Materials Science and Chemistry, Graduate School of Engineering,
University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280
2Goi Research Center, Chisso Petrochemical Corporation, 5-1 Goikaigan, Ichihara, Chiba 290-8551
(Received June 2, 2010; CL-100520; E-mail: kitamura@eng.u-hyogo.ac.jp)
Two 1,4,8,11-tetraalkyl-6,13-diphenylpentacenes were pre-
Me
Me
Me
Me
Me
O
O
O
pared. X-ray analysis revealed that the methyl derivative had
a herringbone arrangement with ³-overlap, while the propyl
derivative had a slipped-parallel structure without ³-overlap.
The solid-state order reflected UV-vis absorption spectra in the
solid state.
OH
OH
1) Et2O
LiAlH4
O
O
+
2) conc. H2SO4
Me
O
O
2
3a (52%)
4a (96%)
Pr
Pr
Pr
Pr
O
COOMe
OH
OH
DMAD
LiAlH4
SO2
O
+
COOMe
Pr
O
Pr
Pr
Pr
5
6
3b
4b (38% in 2 steps)
Pentacene has attracted much attention as a p-type organic
semiconductor, because of the high field-effect transistor (FET)
mobilities of its crystals and thin films.1 However, pentacene is
insoluble in common organic solvents, and the development of
solution-processing electronic devices is desired. Therefore, a
number of soluble pentacene derivatives with substituents have
been prepared.2,3 For instance, Anthony et al. prepared a variety
of 6,13-disubstituted pentacenes, whose substituents contained
functionalized ethyne units. Interestingly, the substituents con-
trolled the solid-state order that is a significant factor in the
R
R
R
O
S
OH
OH
Br
Br
PBr3
HOCH2SO2Na, Bu4NBr
O
R
4a, 4b
a: R = Me, b: R = Pr
R
R
8a (85%), 8b (61%)
7a (93%), 7b (88%)
R
R
O
R
R
R
O
R
X
X
Br2
p-benzoquinone
benzene, reflux
X
O
R
O
R
9a (42%), 9b (49%)
10a, 10b
X = H or Br
R
Ph OH
R
SnCl2, conc. HCl
1) PhLi
performance of FET devices.3 Nuckolls et al. reported an X-ray
1a (77%), 1b (92%)
2) n-BuLi
3) 5% AcOH
¹1
crystal structure and a poor hole mobility (8 © 10¹5 cm2 V¹1 s
)
R
Ph OH
R
of 6,13-diphenylpentacene,2g which had first been prepared in
1942.4 We were impressed particularly by the unique crystal
structure, which displayed that the pentacene cores in a column
direction were arranged cofacially, although the long molecular
axes of nearest neighboring acenes were orthogonal. Addition-
ally, the intermolecular distance between pentacene planes
was ca. 5.0 ¡.2g As a result, there was no ³-overlap between
pentacene frameworks, but only edge-to-face interactions be-
tween phenyl and pentacene rings.
11a (43% from 9a), 11b (37% from 9b)
Scheme 1. Synthesis of pentacecenes 1a and 1b.
1a and 1b were prepared as shown in Scheme 1.6 First, we
thought that the synthesis could be achieved via a reaction
of PhLi and 1,4,8,11-tetraalkyl-6,13-pentacenequinones, which
was prepared using a method proposed by Hanack et al.7 Since
the key intermediates were 3,6-dialkyl-1,2-bis(bromomethyl)-
benzenes 7a and 7b, we prepared the o-xylene-¡,¡¤-diols 4a and
4b as precursors. The methyl derivative 4a was prepared from a
Diels-Alder reaction-dehydration sequence between 2,5-di-
methylfuran (2) and maleic anhydride according to a literature
procedure.8 Although the propyl derivative 4b could be obtained
using the same procedure, the overall yield was poor (<20%)
and the procedure was not always suitable for large-scale
synthesis. We carried out an improved synthesis of 4b using first
a Diels-Alder reaction-desulfonation sequence between 2,5-
dipropylthiophene-1,1-dioxide (5) and dimethyl acetylenedicar-
boxylate (DMAD) at 180 °C, which produced a mixture of
phthalate ester 6 and phthalic anhydride 3b, and subsequently,
a LiAlH4 reduction. The o-xylene-¡,¡¤-diols 4a and 4b were
treated with PBr3 to give dibromides 7a and 7b, respectively.
The reaction of 7a and 7b with HOCH2SO2Na (rongalite) in the
presence of a catalytic amount of Bu4NBr provided 1,4-dihydro-
2,3-benzooxathiin-3-oxides 8a and 8b, which were o-quinodi-
methane synthetic equivalents.9 Alkyl-substituted octahydropen-
tacenequinones 9a and 9b were obtained by heating 8a and 8b
with 0.4 equiv of p-benzoquinone in refluxing benzene. Next,
oxidation of 9a and 9b with 10 equiv of Br2 resulted in not only
Since it is recognized that the solid-state order can
significantly affect charge transport properties as well as
intermolecular interactions, the control of stacking arrays of
acene moieties is a critical issue for electronic devices. Recently,
we prepared a series of alkyl-substituted tetracenes on the
terminal benzene rings.5 We found that the alkyl side chains had
abilities to tune both molecular arrangements and photophysical
properties in the solid state. To metamorphose the unique
stacking pattern of 6,13-diphenylpentacene mentioned above,
we introduced alkyl side chains onto the terminal A and E rings
in pentacene (Figure 1). We report here the synthesis and crystal
structures of 6,13-diphenylpentacene derivatives 1a and 1b
having methyl and propyl groups, respectively, at the 1-, 4-, 8-,
and 11-positions.
R
Ph
R
11
1
13
1a: R = Me
1b: R = Pr
A
B
C
D
E
6
8
4
R
Ph
R
Figure 1. Structures of alkyl-substituted 6,13-diphenylpenta-
cenes.
Chem. Lett. 2010, 39, 771-773
© 2010 The Chemical Society of Japan