794
Chemistry Letters Vol.36, No.6 (2007)
Rod-shaped Oligophenyleneethynylenes Modified by Donor and Acceptor Groups
in a Block Manner: Synthesis and Light-emitting Characteristics
Takanori Ochi, Yoshihiro Yamaguchi,ꢀ Shigeya Kobayashi, Tateaki Wakamiya,
Yoshio Matsubara, and Zen-ichi Yoshidaꢀ
Department of Chemistry, Kinki University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502
(Received April 9, 2007; CL-070378; E-mail: yamaguch@chem.kindai.ac.jp, yoshida@chem.kindai.ac.jp)
NC
NC
NC
1
Highly efficient blue light emmitters represented by BL-5
OMe
5
OMe
OMe
3
OMe
OMe
NC
OMe
NC
(ꢀf ¼ 0:96, ꢁem ¼ 455 nm in CHCl3) and BL-8 (ꢀf ¼ 0:98,
ꢁem ¼ 464 nm in CHCl3) are created by block modification
of oligophenylene ethynylenes with donor and acceptor groups.
A linear relationship with positive slope between ꢀf and the
movability of the energetically equivalent dipolar structure unit
is found for the first time.
2
4
NC
NC
NC
NC
OMe
OMe
OMe
OMe
BL-3
BL-1
BL-2
NC
NC
NC
NC
NC
The importance of organic light-emitting materials with
high emission efficiency in biological, chemical, and materials
science has been greatly increasing. However, a general concept
or a method for creation of highly fluorescent molecules in a de-
sired wavelength region has not been established yet, though
various attempts to achieve this goal have been made.1 Thus,
the development of method for creation of highly fluorescent
molecules should be an urgent subject. Here, we report synthesis
and light-emitting characteristics of oligophenyleneethynylenes
modified by donor and acceptor groups in a block manner
(BL-1–BL-8, see Figure 1) together with a relationship between
quantum yield (ꢀf) and the movability of the energetically
equivalent dipolar structure unit (so-called intramolecular
exciton2) in the excited singlet state.
Synthesis of block modification system (BL-1–BL-8) was
made in the following order using the Pd C–C coupling reaction3
as the key step: (1) preparation of acceptor blocks (1 and 2), (2)
preparation of donor blocks (3, 4, and 5), and (3) cross-coupling
reaction between donor blocks and acceptor blocks (Figure 2,
further detail, see the Electronic Supporting Information).7 The
structures of BLs were confirmed by spectral data (1H and
13C NMR spectroscopy and HR-FAB MS, see the Electronic
Supporting Information).7
OMe
OMe
BL-4
OMe
OMe
OMe
OMe
BL-5
NC
NC
NC
OMe
OMe
OMe
OMe
BL-7
BL-6
NC
NC
NC
OMe
OMe
OMe
BL-8
Figure 2. Structures of donor blocks, acceptor blocks, and
block modification system (BL-1–BL-8).
emission lifetime (ꢂ) are summarized in Table 1. The kr and
kd were calculated from ꢂ and ꢀf.4
As shown in Table 1, it is demonstrated that the ꢀf and ꢁem
values increase effectively by the block modification, though ꢀf
values increase essentially with the ꢃ-conjugation length even
for the parent system. Thus, very high ꢀf values (>0:95) and
emission at longer wavelength (>430 nm) are observed for the
block modification system such as BL-4 (n ¼ ðl þ mÞ ꢁ 1 ¼
2), BL-5 (n ¼ ðl þ mÞ ꢁ 1 ¼ 3), BL-7 (n ¼ ðl þ mÞ ꢁ 1 ¼ 3),
The photophysical data of block modification system
(BL-1–BL-8), and parent system (PR-1–PR-3)1c together with
radiative rate constant (kr), radiationless rate constant (kd), and
Table 1. Photophysical data of block modification system and
parent system in chloroforma
Com-
pound
ꢁem Stokes
ꢁabs
ꢂ
kr
/sꢁ1
kd
/sꢁ1
b
n
ꢀf
log "
/nm shift/nm /nm /ns
Parent system
H
BL-1
BL-2
BL-3
BL-4
BL-5
BL-6
BL-7
BL-8
PR-1
PR-2
PR-3
1
2
1
2
3
2
3
4
1
2
3
0.82 403
0.93 419
0.84 392
0.95 434
0.96 455
0.95 407
0.98 443
0.98 464
0.50 348
0.61 387
0.83 388
45
49
40
54
69
42
56
72
20
42
38
4.61 358 2.45 3:34 ꢂ 108 7:33 ꢂ 107
4.87 370 1.35 6:89 ꢂ 108 5:19 ꢂ 107
4.66 352 2.19 3:84 ꢂ 108 7:31 ꢂ 107
4.81 380 1.55 6:13 ꢂ 108 3:23 ꢂ 107
4.92 386 1.20 7:98 ꢂ 108 3:33 ꢂ 107
4.90 365 1.25 7:57 ꢂ 108 3:99 ꢂ 107
4.96 387 1.10 8:94 ꢂ 108 1:82 ꢂ 107
4.99 392 1.02 9:58 ꢂ 108 1:95 ꢂ 107
4.59 328 2.57 1:95 ꢂ 108 1:95 ꢂ 108
4.77 345 1.70 3:59 ꢂ 108 2:30 ꢂ 108
4.80 350 1.58 5:24 ꢂ 108 1:07 ꢂ 108
n
PR - 1: n = 1, PR - 2: n = 2, PR - 3: n = 3
MeO
MeO
NC
Block modification system
H
m
l
BL - 1: n = 1 (l = 0, m = 2), BL - 2: n = 2 (l = 0, m = 3)
BL - 3: n = 1 (l = 1, m = 1), BL - 4: n = 2 (l = 1, m = 2), BL - 5: n = 3 (l = 1, m = 3)
BL - 6: n = 2 (l = 2, m = 1), BL - 7: n = 3 (l = 2, m = 2), BL - 8: n = 4 (l = 2, m = 3)
* n:Total number of the substituted phenylene ethynylene unit
( n = (l + m) - 1 for the block modification system)
aAll spectra were measured at 295 K. bQuantum yield is calculated relative to
Figure 1. Structures of the parent (PR) system and the block
modification (BL) system.
quinine (ꢀf ¼ 0:55 in 0.1 M H2SO4).
Copyright Ó 2007 The Chemical Society of Japan