Effect of phenyl ring substitution on J-aggregate formation ability of novel bisazomethine dyes in vapour-deposited films

Article abstract of DOI:10.1016/j.dyepig.2010.11.009

Bisazomethine dyes, which are synthesized using diaminomaleonitrile and aminobenzaldehydes, exhibit red fluorescence in solution and in the solid state. Several bisazomethine dyes are known to form J-aggregates in vapour-deposited films. In this work, novel bisazomethine dyes were synthesized and the effect of phenyl ring substitution on the J-aggregate formation in vapour-deposited films was examined. The optical properties of the dyes were examined in solution and in the solid state through molecular orbital calculations. Four derivatives were found to form J-aggregates in vapour-deposited films as determined from the shape of the spectrum and the absorption edge.

Full text of DOI:10.1016/j.dyepig.2010.11.009

Dyes and Pigments 90 (2011) 56e64
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Effect of phenyl ring substitution on J-aggregate formation ability of novel
bisazomethine dyes in vapour-deposited films
,
,b,
*
Byung-Soon Kim a, Daisuke Kashibuchi b, Young-A Son c, Sung-Hoon Kim d e, Shinya Matsumoto a
a Graduate School of Environmental and Information Sciences, Yokohama National University, Hodogaya-ku, Yokohama 240-8501, Japan
b Faculty of Education and Human Sciences, Yokohama National University, Hodogaya-ku, Yokohama 240-8501, Japan
c School of Chemical and Biological Engineering, Chungnam National University, Daejeon 305-764, Republic of Korea
d Department of Textile System Engineering, Kyungpook National University, Daegu 702-701, Republic of Korea
e School of Chemical Science & Technology, Zhanjiang Normal University, Zhanjiang 524048, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Bisazomethine dyes, which are synthesized using diaminomaleonitrile and aminobenzaldehydes, exhibit
red fluorescence in solution and in the solid state. Several bisazomethine dyes are known to form J-
aggregates in vapour-deposited films. In this work, novel bisazomethine dyes were synthesized and the
effect of phenyl ring substitution on the J-aggregate formation in vapour-deposited films was examined.
The optical properties of the dyes were examined in solution and in the solid state through molecular
orbital calculations. Four derivatives were found to form J-aggregates in vapour-deposited films as
determined from the shape of the spectrum and the absorption edge.
Received 15 September 2010
Received in revised form
16 November 2010
Accepted 17 November 2010
Available online 30 November 2010
Keywords:
Bisazomethine dye
J-aggregates
Ó 2010 Elsevier Ltd. All rights reserved.
Vapour-deposited film
Optical properties
Molecular orbital calculations
1. Introduction
being J-aggregates. J-aggregates are characterized by sharp red-shifted
absorption and strong photoluminescence with respect to the corre-
In recent years, organic molecular materials have gained consid-
erable importance from the viewpoint of their applications in opto-
electronics: these materials can be used to fabricate optoelectronic
devices such as organic light-emitting diodes, organic thin-film tran-
sistors, and organic solar cells [1e9]. Devices fabricated using organic
molecular materials are expected to be lightweight and flexible;
moreover, the fabricationprocessis environmentally friendly [10e12].
Many studies have focused on the development of novel organic
molecular materials for the abovementioned applications [13,14] with
the aim of obtaining devices with high performance characteristics.
However, it is difficult to design the solid-state structure of organic
molecules with the desired properties. This is because very little is
known about the crystallization phenomena of organic molecules.
Molecular aggregates have attracted considerable attention as
potential candidates for improving the characteristics of optoelectronic
devices, with the most well-known example of molecular aggregates
sponding molecular electronic states [15e22]. These characteristic
features are attributed to the excitonic interaction within the
aggregates [23]. Scheibe [24] and Khun [25] reported plausible
low-dimensional molecular arrangements of J-aggregates. Kato
experimentally demonstrated that merocyanine J-aggregates have
a brick-wall arrangement in an LB-film and that the electronic states of
the film can be interpreted on the basis of exciton interaction [17].
In this study, we have synthesized bisazomethine dyes by using
diaminomaleonitrile and benzaldehydes. Crystal structure studies
on some bisazomethine dyes [26e28] have revealed that this dye
system has a potential to form J-aggregates [20,22,29]. The spectra of
several bisazomethine dyes in vapour-deposited films were
remarkably different from those of their solutions; the spectra in the
formercase showed a sharp absorption bandin the long-wavelength
region [30,31]. For N, N0-bis[4-(N, N-diethylamino)benzylidene]-
diaminomaleonitrile (DE2), this band was assigned to J-aggregates
[31]. J-aggregate films of DE2, however, also include a non-aggregate
solidphase corresponding tothe singlecrystal phase[26]. This phase
mixing was thought to be the cause of the weak fluorescence of J-
aggregate films of DE2 [32]. In a previous study, we examined the
photovoltaic properties of J-aggregate films of DE2; although we did
not find an apparent contribution of J-aggregates in the
* Corresponding author. Faculty of Education and Human Sciences, Yokohama
National University, Hodogaya-ku, Yokohama 240-8501, Japan. Tel.: þ81 45 339
3366; fax: þ81 45 339 3345.
E-mail address: smatsu@edhs.ynu.ac.jp (S. Matsumoto).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.11.009

B.-S. Kim et al. / Dyes and Pigments 90 (2011) 56e64
57
photocurrent action spectra of the films, we found that the films are
a potential photocarrier-generating material comparable to metal
phthalocyanines [33]. Thus, it may be possible to improve the solid-
state properties of this dye system by using a pure J-aggregate solid
film. This report describes the effect of phenyl ring substitution on J-
aggregate formation in vapour-deposited films. The dyes were
synthesized by the reaction of diaminomaleonitrile with 4-(dime-
thylamino)-2-alkoxybenzaldehydes (1ae7a) and 4-(diethylamino)-
2-alkoxybenzaldehydes (8ae14a). The UVeVis absorption and
fluorescent properties of the synthesized dyes were investigated in
solution as well as in vapour-deposited films. The electronic states of
the dyes were characterized by molecular orbital calculations.
phenol 20 mmol (2.75 g) and 10 ml N, N-dimethylformamide was
dropwise added 42 mmol phosphorus oxychloride (3.46 g) at 0 ꢂC
while stirring. The resulting mixture was stirred at 80 ꢂC for 16 h.
After 16 h, the reaction was cooled to room temperature and the
mixture was quenched into 150 ml ice water. The formed precipitate
solution was adjusted to the neutral pH condition using 4 M sodium
hydroxide solution. The solid was filtered and purified by column
chromatography by eluting with ethyl acetate/n-hexane (ethyl
acetate:n-hexane ¼ 1:3 v/v). The yellow solid was obtained after
recrystalization with n-hexane. Yield: 61.2% (2.02 g); M.p. 78e79 ꢂC
1H NMR (300 MHZ, CDCl3):
d10.73 (s, 1H, CHO),
d8.64 (s, 1H, OH),
d
6.38e6.43 (t, J ¼ 8.8 Hz, 1H, aromatic),
d
5.40e5.44 (dd, J ¼ 6.6 and
2.3 Hz, 1H, aromatic),
d
5.21e4.22 (d, J ¼ 2.3 Hz, 1H, aromatic),
2. Experimental
d
2.17e2.19 (d, J ¼ 5.0 Hz, 6H, NMe2); IR (KBr): 1646 (C]O) cmꢁ1
.
A
mixture of 10 mmol 4-(dimethylamino)salicylaldehyde
2.1. Materials and equipment
(1.66 g) (or 4-(diethylamino)salicylaldehyde (1.94 g)) and 20 mmol
potassium carbonate (2.76 g) was dissolved in 30 ml dry DMF. To
this mixture was added 30 mmol alkyl bromide and the mixture
was refluxed for 8 h at 50 ꢂC. The reaction mixture was cooled to
room temperature and filtered to remove potassium carbonate. The
mixture was then poured into ice water and extracted with ethyl
acetate. The combined organic layer was washed with water and
brine and dried over magnesium sulphate. The solvent was evap-
orated under reduced pressure and then purified by column chro-
matography by eluting with ethyl acetate/n-hexane (ethyl
acetate:n-hexane ¼ 1:3 v/v) and recrystalization with n-hexane.
These bright brown compounds 1ae14a were found to melt around
30e32 ꢂC. To obtain 2a and 9a, 10 mmol of copper (I) oxide (1.43 g)
was added as a catalyst and the reaction conditions were changed
to 5 h and 100 ꢂC 1a [41e43], Yield: 87.6% (2.24 g); 1H NMR
3-(Dimethylamino)phenol (97%) and 4-(diethylamino)salicy-
laldehyde (98%) were purchased from SigmaeAldrich Co. Alkyl-
bromides (98%) and diaminomaleonitrile (98%) were obtained from
Wako Pure Chem. Ind., Ltd. and Nacalai Tesque Inc., respectively.
Wakogel C-300 (silica gel) was used for the column chromatography.
The 1H NMR spectra were recorded on an EX 270 MHz NMR instru-
ment(JeolLtd.)andaDRX300MHzNMRinstrument(BrukerCo.)with
TMS as the internal standard. The elemental analyses were recorded
on a Vario EL III elemental analyzer (Elementar Co.). The IR spectra
were recorded using a PerkinElmer Spectrum BX FTIR system spec-
trophotometer. The absorption spectra of the bisazomethine dyes and
those of their vapour-deposited films were determined using a Per-
kinElmer Lambda 20 UVeVis spectrophotometer and a PerkinElmer
Lambda 750 UVeVis spectrophotometer, respectively. Fluorescence
spectra measurements were performed on an LS 45 spectrofluorim-
eter (PerkinElmer) equipped with a xenon discharge lamp and 1-cm
quartz cells. The fluorescence spectra of the vapour-deposited films
were recorded using an LS 55 spectrofluorimeter (PerkinElmer). The
concentration of the solutions used for absorption and fluorescence
measurements was ca. 1.0 ꢀ 10ꢁ5 M. Thermal analysis of the synthe-
sized dyes was carried out by using a MEL-TEMP electrothermal
melting point apparatus without corrections. Thin films of the
synthesized novel bisazomethine dyes were vapour-deposited onto
a glass substrate using vacuum deposition equipment (ULVAC VPC-
060) under vacuum conditions of ca. 3.0 ꢀ 10ꢁ2 Pa. All measurements
were taken at room temperature at approximately 298 K.
(300 MHz, CDCl3):
d
10.21 (s, 1H, CHO),
7.27e7.40 (m, 5H, OeBz),
6.26 (d, J ¼ 1.5 Hz, 1H, aromatic),
d
7.68e7.71 (d, J ¼ 8.8 Hz, 1H,
6.29 (d, J ¼ 1.5 Hz, 1H,
5.11 (s, 2H, OeBz),
aromatic),
aromatic),
d
d
d
d
d
2.99 (s, 6H, NMe2); IR (KBr): 1651 (C]O) cmꢁ1. 2a [44e46], Yield:
33.2% (0.80 g); 1H NMR (300 MHz, CDCl3):
CHO),
7.76e7.79 (d, J ¼ 8.8 Hz, 1H, aromatic),
OePh), 6.97e7.09 (m, 3H, OePh),
6.43e6.47 (dd, J ¼ 6.4 and
2.4 Hz, 1H, aromatic), 2.92
5.99e6.00 (d, J ¼ 2.5 Hz, 1H, aromatic),
(s, 6H, NMe2); IR (KBr): 1664 (C]O) cmꢁ1. 3a, Yield: 68.1% (1.22 g);
1H NMR (270 MHz, CDCl3):
10.15 (s, 1H, CHO), 7.69e72 (d,
J ¼ 8.1 Hz, 1H, aromatic), 6.27e6.31 (dd, J ¼ 8.1 and 2.7 Hz, 1H,
aromatic), 6.01e6.02 (s, 1H, aromatic), 3.89 (s, 3H, OeMe), 3.07
(s, 6H, NMe2); IR (KBr): 1656 (C]O) cmꢁ1. 4a, Yield: 52.6% (1.09 g);
1H NMR (270 MHz, CDCl3):
10.23 (s, 1H, CHO), 7.72e75 (d,
J ¼ 8.1 Hz, 1H, aromatic), 6.28e6.32 (dd, J ¼ 8.1 and 2.7 Hz, 1H,
aromatic), 3.99e4.03 (t,
6.03e6.04 (d, J ¼ 2.7 Hz, 1H, aromatic),
d10.10e10.11 (s, 1H,
d
d7.27e7.34 (m, 2H,
d
d
d
d
d
d
d
d
d
d
d
d
2.2. Molecular orbital calculations
d
d
d
The molecular structure for the calculation of the electronic states
of a molecule was optimized by using the AM1 Hamiltonian [34].
Theoretical absorption properties were obtained by the INDO/S
Hamiltonian [35,36] on the basis of the optimized molecular struc-
ture. 257 configuration interactions were taken into account. All the
calculations were performed with a CAChe 5.2 program package [37].
J ¼ 5.4 Hz, 2H, OePr),
d3.07 (s, 6H, NMe2), d1.80e1.93 (m, 2H, OePr),
d
1.04e1.10 (t, J ¼ 5.4 Hz, 3H, OePr); IR (KBr): 1660 (C]O) cmꢁ1. 5a,
Yield: 64.9% (1.44 g); 1H NMR (270 MHz, CDCl3):
d10.21 (s, 1H,
CHO),
aromatic),
J ¼ 6.2 Hz, 2H, OeBu),
OeBu), 1.45e1.59 (m, 2H, OeBu),
OeBu); IR (KBr): 1660 (C]O) cmꢁ1. 6a, Yield: 67.6% (1.59 g); 1H
NMR (300 MHz, DMSO-d6): 10.05 (s, 1H, CHO), 7.49e7.52 (d,
J ¼ 8.8 Hz, 1H, aromatic), 6.34e6.37 (dd, J ¼ 9.0 and 1.5 Hz, 1H,
aromatic), 4.06e4.11 (t,
6.17e6.18 (d, J ¼ 2.2 Hz, 1H, aromatic),
J ¼ 6.4 Hz, 2H, OePen), 3.04 (s, 6H, NMe2), 1.74e1.79 (m, 2H,
OePen), 1.34e1.39 (m, 4H, OePen),
0.87e0.92 (t, J ¼ 7.0 Hz, 3H,
OePen); IR (KBr): 1661 (C]O) cmꢁ1. 7a, Yield: 56.1% (1.71 g); 1H
NMR (300 MHz, DMSO-d6): 10.05 (s, 1H, CHO), 7.49e7.52 (d,
J ¼ 8.8 Hz, 1H, aromatic), 6.33e6.36 (d, J ¼ 8.8 Hz, 1H, aromatic),
6.16e6.17 (d, J ¼ 2.3 Hz,1H, aromatic), 4.06e4.10 (t, J ¼ 6.4 Hz, 2H,
OeDec), 3.04 (s, 6H, NMe2), 1.72e1.77 (m, 2H, OeDec),
1.24e1.43 (m, 14H, OeDec),
0.82e0.86 (t, J ¼ 6.4 Hz, 3H, OeDec);
d
7.70e7.74 (d, J ¼ 8.9 Hz, 1H, aromatic),
6.02e6.03 (d, J ¼ 2.1 Hz, 1H, aromatic),
3.06 (s, 6H, NMe2), 1.77e1.87 (m, 2H,
0.96e1.01 (t, J ¼ 7.3 Hz, 3H,
d
6.26e6.30 (m, 1H,
d
d4.02e4.07 (t,
d
d
d
d
2.3. Synthesis and characterization
d
d
Novel bisazomethine dyes were synthesized according to
a previously described method [38,39], and their chemical struc-
ture was confirmed by 1H NMR, IR, and elemental analysis. The
synthetic procedure is illustrated in Scheme 1.
d
d
d
d
d
d
d
2.3.1. 4-(Dimethylamino)salicylaldehyde, 4-(dimethylamino)-
2-alkoxybenzaldehydes 1ae7a and 4-(diethylamino)-
2-alkoxybenzaldehydes 8ae14a
4-(Dimethylamino)salicylaldehyde was synthesized by the
reported procedure [40]. To the mixture of 3-(dimethylamino)
d
d
d
d
d
d
d
d
d

58
B.-S. Kim et al. / Dyes and Pigments 90 (2011) 56e64
Scheme 1.
IR (KBr): 1664 (C]O) cmꢁ1. 8a, Yield: 35.0% (0.99 g); 1H NMR
(270 MHz, CDCl3): 10.23 (s, 1H, CHO),
7.24e7.45 (m, 5H, OeBz),
5.16 (s, 2H, OeBz),
3.31e3.39 (q, J ¼ 7.2 Hz, 4H, NEt2),
Yield: 72.9% (1.92 g); 1H NMR (270 MHz, CDCl3):
7.69e7.72 (d, J ¼ 8.1 Hz, 1H, aromatic), 6.24e6.28 (dd, J ¼ 5.4 and
2.7 Hz, 1H, aromatic),
6.01e6.02 (d, J ¼ 2.7 Hz, 1H, aromatic),
3.37e3.45 (q, J ¼ 8.1 Hz, 4H,
1.38e1.51 (m, 4H, OePen),
0.91e0.95 (t, J ¼ 6.7 Hz, 3H,
OePen); IR (KBr): 1661 (C]O) cmꢁ1. 14a, Yield: 55.7% (1.86 g); 1H
NMR (270 MHz, CDCl3): 10.18 (s, 1H, CHO), 7.70e7.73 (d,
J ¼ 8.1 Hz, 1H, aromatic), 6.25e6.29 (m, 1H, aromatic), 6.01e6.02
(d, J ¼ 2.7 Hz, 1H, aromatic), 4.00e4.05 (t, J ¼ 6.7 Hz, 2H, OeDec),
3.38e3.46 (q, J ¼ 8.1 Hz, 4H, NEt2), 1.78e1.88 (m, 2H, OeDec),
1.11e1.51 (m, 20H, OeDen and NEt2),
0.86e0.91 (t, J ¼ 5.4 Hz, 3H,
OeDec); IR (KBr): 1661 (C]O) cmꢁ1
d10.19 (s,1H, CHO),
d
d
7.71e7.74 (d, J ¼ 8.8 Hz, 1H,
d
d
aromatic),
aromatic),
d
d
d
d6.12e6.32 (d, J ¼ 8.2 Hz, 2H,
d
d
d
4.00e4.05 (t, J ¼ 6.7 Hz, 2H, OePen),
d
1.06e1.23 (m, 6H, NEt2); IR (KBr): 1644 (C]O) cmꢁ1. 9a, Yield:
NEt2), d1.78e1.88 (m, 2H, OePen), d
30.0% (0.81 g); 1H NMR (300 MHz, CDCl3):
d
10.13 (s, 1H, CHO),
7.33e7.38 (m, 2H, OePh),
6.47e6.50 (d, J ¼ 9.0 Hz, 1H, aromatic),
6.02e6.03 (d, J ¼ 2.0 Hz, 1H, aromatic), 3.28e3.35 (q, J ¼ 7.1 Hz,
1.10e1.14 (t, J ¼ 6.9 Hz, 6H, NEt2); IR (KBr): 1658 (C]
O) cmꢁ1. 10a, Yield: 84.8% (1.76 g); 1H NMR (300 MHz, CDCl3):
d1.19e1.24 (t, J ¼ 6.7 Hz, 6H, NEt2),
d
d
d
d
7.80e7.83 (d, J ¼ 8.8 Hz, 1H, aromatic),
d
7.03e7.14 (m, 3H, OePh),
d
d
d
d
d
d
4H, NEt2),
d
d
d
d
d
d
d
10.11e10.12 (s, 1H, CHO),
6.26e6.29 (dd, J ¼ 7.1 and 1.6 Hz, 1H, aromatic),
3.88 (s, 3H, OeMe),
1.15e1.24 (t, J ¼ 7.0 Hz, 6H, NEt2); IR (KBr):
1645 (C]O) cmꢁ1. 11a, Yield: 84.9% (1.88 g); 1H NMR (270 MHz,
CDCl3): 10.17 (s, 1H, CHO),
7.69e7.72 (d, J ¼ 8.9 Hz, 1H, aromatic),
6.25e6.28 (m, 1H, aromatic),
6.01e6.02 (d, J ¼ 2.4 Hz, 1H,
aromatic), 3.37e3.45 (q,
4.06e4.14 (q, J ¼ 7.0 Hz, 2H, OeEt),
1.18e1.23
d
7.68e7.71 (d, J ¼ 8.8 Hz, 1H, aromatic),
6.02e6.03 (d,
3.39e3.46 (q,
d
d
.
J ¼ 2.4 Hz, 1H, aromatic),
J ¼ 7.1 Hz, 4H, NEt2),
d
d
2.3.2. Bisazomethine dyes 1be14b
To 15 ml of benzene was added a mixture of 0.5 mmol
diaminomaleonitrile (0.06 g) and 1.0 mmol of the prepared
4-(dimethylamino)-2-alkoxybenzaldehydes (or 4-(diethylamino)-
2-alkoxybenzaldehydes); the resulting mixture was stirred. Piperi-
dine was added dropwise during the reaction. Reflux was continued
for 8 h with a Dean-Stark trap. After 8 h, the reaction mixture was
cooled to room temperature. The precipitated crude product was
filtered and washed with methanol. The product was then purified
by column chromatography using chloroform. The purple solids
were obtained after recrytallization from chloroform except for dyes
7b and 14b which gave red solids. 1b, Yield: 62.0% (0.18 g); M.p.
310e311 ꢂC. Anal. Calcd for C36H34N6O2: C, 74.20; H, 5.88; N, 14.42.
d
d
d
d
d
d
J ¼ 7.0 Hz, 4H, NEt2),
d
1.43e1.48 (t, J ¼ 7.0 Hz, 3H, OeEt),
d
(t, J ¼ 7.0 Hz, 6H, NEt2); IR (KBr): 1652 (C]O) cmꢁ1.12a, Yield: 77.3%
(1.82 g); 1H NMR (300 MHz, CDCl3):
d10.19 (s, 1H, CHO), d7.70e7.73
(d, J ¼ 9.0 Hz, 1H, aromatic),
aromatic),
6.01 (d, J ¼ 2.2 Hz, 1H, aromatic),
3.38e3.45 (q, J ¼ 7.1 Hz, 4H, NEt2),
d
6.25e6.29 (dd, J ¼ 7.3 and 1.7 Hz, 1H,
d
d
3.97e4.01 (t,
J ¼ 6.4 Hz, 2H, OePr),
d
d
1.80e1.92 (m, 2H, OePo),
d
1.19e1.24 (t, J ¼ 7.1 Hz, 6H, NEt2),
d
1.10e1.14 (t, J ¼ 7.4 Hz, 3H, OePr); IR (KBr): 1655 (C]O) cmꢁ1. 13a,

B.-S. Kim et al. / Dyes and Pigments 90 (2011) 56e64
59
Found: C, 74.12; H, 5.78; N,14.13.1H NMR (300 MHz, CDCl3):
d
9.15 (s,
7.37e7.48 (m,
6.34e6.38 (dd, J ¼ 6.4 and 2.5 Hz, 2H, aromatic),
J ¼ 2.2 Hz, 2H, aromatic),
d
3.88 (s, 6H, OeMe),
d
3.41e3.49 (q,
2H, CH]N),
10H, OeBz),
d
d
8.14e8.17 (d, J ¼ 9.0 Hz, 2H, aromatic),
d
J ¼ 7.0 Hz, 8H, NEt2), 1.21e1.26 (t, J ¼ 7.3 Hz, 12H, NEt2); IR (KBr):
d
2201 (C^N) cmꢁ1,1610 (CH]N) cmꢁ1.11b, Yield: 71.7% (0.18 g); M.p.
d
6.08e6.09 (d, J ¼ 2.3 Hz, 2H, aromatic),
d5.22 (s, 4H, OeBz), d3.05 (s,
258e259 ꢂC. Anal. Calcd for C30H38N6O2: C, 70.01; H, 7.44; N, 16.33:
12H, NMe2); IR (KBr): 2208 (C^N) cmꢁ1, 1615 (CH]N) cmꢁ1. 2b,
Yield: 64.3% (0.18 g); M.p. 312e313 ꢂC. Anal. Calcd for C34H30N6O2: C,
73.63; H, 5.45; N, 15.15. Found: C, 72.79; H, 5.39; N, 15.0. 1H NMR
Found; C, 69.78; H, 7.44; N,16.27.1H NMR (300 MHz, CDCl3):
d
9.01 (s,
6.33e6.36 (dd,
6.03e6.04 (d, J ¼ 3.0 Hz, 2H,
4.08e4.15 (dd, J ¼ 9.0 and 6.0 Hz, 4H, OeEt), 3.40e3.47
2H, CH]N),
J ¼ 9.0 and 2.1 Hz, 2H, aromatic),
aromatic),
d
8.10e8.13 (d, J ¼ 9.0 Hz, 2H, aromatic),
d
d
(270 MHz, CDCl3):
J ¼ 9.1 Hz, 2H, aromatic),
6H, OePh),
6.55e6.60 (dd, J ¼ 7.0 and 2.2 Hz, 2H, aromatic),
d9.01e9.06 (s, 2H, CH]N),
d8.20e8.23 (d,
d
d
d7.32e7.38 (m, 4H, OePh),
d7.07e7.16 (m,
(q, J ¼ 6.0 Hz, 8H, NEt2), 1.47e1.51 (t, J ¼ 6.0 Hz, 6H, OeEt),
d
d
d
1.21e1.25 (t, J ¼ 6.0 Hz,12H, NEt2); IR (KBr): 2203 (C^N) cmꢁ1,1609
d
6.12e6.13 (d, J ¼ 2.4 Hz, 2H, aromatic),
d2.98e3.08 (m,12H, NMe2);
(CH]N) cmꢁ1. 12b, Yield: 71.8% (0.19 g); M.p. 302e304 ꢂC. Anal.
IR (KBr): 2207 (C^N) cmꢁ1, 1612 (CH]N) cmꢁ1. 3b, Yield: 70.9%
(0.15 g); M.p. 318e320 ꢂC. Anal. Calcd for C24H26N6O2: C, 66.96; H,
6.09; N, 19.52. Found: C, 66.89; H, 6.08; N, 19.50. 1H NMR (270 MHz,
Calcd for C32H42N6O2: C, 70.82; H, 7.80; N,15.49: Found; C, 70.02; H,
7.72; N, 15.12. 1H NMR (300 MHz, CDCl3):
d
9.02 (s, 2H, CH]N),
6.32e6.36 (dd, J ¼ 7.2 and
3.97e4.02
d
8.09e8.12 (d, J ¼ 9.0 Hz, 2H, aromatic),
d
CDCl3):
d
9.03 (s, 2H, CH]N),
d
8.12e8.15 (d, J ¼ 8.9 Hz, 2H, aromatic),
2.1 Hz, 2H, aromatic),
(t, J ¼ 6.5 Hz, 4H, OePr),
d
6.03 (d, J ¼ 2.3 Hz, 2H, aromatic),
d
d
6.38 (dd, J ¼ 7.1 and 2.1 Hz, 2H, aromatic),
d
6.04e6.05 (d, J ¼ 2.0 Hz,
d
d
3.40e3.47 (q, J ¼ 7.2 Hz, 8H, NEt2),
2H, aromatic),
d3.90 (s, 6H, OeMe),
d3.11 (s, 12H, NMe2); IR (KBr):
d
d
1.86e1.93 (m, 4H, OePr),
1.20e1.25 (t, J ¼ 7.1 Hz, 12H, NEt2),
2203 (C^N) cmꢁ1,1608 (CH]N) cmꢁ1. 4b, Yield: 46.5% (0.11 g); M.p.
1.07e1.12 (t, J ¼ 7.3 Hz, 6H, OePr); IR (KBr): 2201 (C^N) cmꢁ1,1612
320e321 ꢂC. Anal. Calcd for C28H34N6O2: C, 69.11; H, 7.04; N, 17.27.
(CH]N) cmꢁ1. 13b, Yield: 60.8% (0.18 g); M.p. 270e271 ꢂC. Anal.
Found: C, 68.86; H, 7.03; N,17.17.1H NMR (270 MHz, CDCl3):
d
9.03 (s,
6.38 (s, 2H,
3.97e4.02 (t,
Calcd for C36H50N6O2: C, 72.21; H, 8.42; N, 14.03: Found; C, 71.92; H,
2H, CH]N),
aromatic),
d
8.12e8.15 (d, J ¼ 8.1 Hz, 2H, aromatic),
d
8.41; N, 13.94. 1H NMR (270 MHz, CDCl3):
d
9.02 (s, 2H, CH]N),
6.31e6.35 (dd, J ¼ 5.4 and
6.03e6.04 (d, J ¼ 2.7 Hz, 2H, aromatic),
3.40e3.47 (dd, J ¼ 8.1 and
1.56e1.90 (m, 4H, OePen), 1.37e1.56 (m, 8H,
d
6.04e6.05 (d, J ¼ 2.7 Hz, 2H, aromatic),
d
d
8.09e8.13 (d, J ¼ 9.5 Hz, 2H, aromatic),
d
J ¼ 6.7 Hz, 4H, OePr),
d3.11 (s,12H, NMe2),
d1.86e1.93 (m, 4H, OePr),
2.7 Hz, 2H, aromatic),
d
d
1.07e1.12 (t, J ¼ 6.8 Hz, 6H, OePr); IR (KBr): 2202 (C^N) cmꢁ1,1611
d
4.01e4.05 (t, J ¼ 5.4 Hz, 4H, OePen),
d
(CH]N) cmꢁ1. 5b, Yield: 60.4% (0.16 g); M.p. 300e302 ꢂC. Anal. Calcd
5.4 Hz, 8H, NEt2),
d
d
for C30H38N6O2: C, 70.01; H, 7.44; N,16.33. Found: C, 70.12; H, 7.48; N,
OePen),
d
1.20e1.25 (t, J ¼5.4 Hz,12H, NEt2), 0.93e0.98(t, J ¼5.4 Hz,
d
16.31.1H NMR (270 MHz, CDCl3):
d
9.04 (s, 2H, CH]N),
6.33e6.37 (dd, J ¼ 7.0 and 2.2 Hz, 2H,
6.04e6.05 (d, J ¼ 2.4 Hz, 2H, aromatic), 4.03e4.08 (t,
J ¼ 6.5 Hz, 4H, OeBu), 3.09 (s, 12H, NMe2), 1.81e1.91 (m, 4H,
OeBu), 1.48e1.61 (m, 4H, OeBu),
d
8.11e8.14 (d,
6H, OePen); IR (KBr): 2201 (C^N) cmꢁ1, 1614 (CH]N) cmꢁ1. 14b,
J ¼ 8.2 Hz, 2H, aromatic),
d
aromatic),
d
d
d
d
d
d
0.98e1.03 (t, J ¼ 7.3 Hz, 6H,
OeBu); IR (KBr): 2202 (C^N) cmꢁ1, 1613 (CH]N) cmꢁ1. 6b, Yield:
72.5% (0.20 g); M.p. 287e289 ꢂC. Anal. Calcd for C32H42N6O2: C,
70.82; H, 7.80; N, 15.49. Found: C, 70.42; H, 7.70; N, 15.49. 1H NMR
(270 MHz, CDCl3):
aromatic),
6.31e6.35 (dd, J ¼ 7.1 and 2.7 Hz, 2H, aromatic),
6.03e6.04 (d, J ¼ 2.7 Hz, 2H, aromatic), 4.01e4.05 (t, J ¼ 5.4 Hz, 4H,
OePen), 3.09 (s, 12H, NMe2), 1.81e1.90 (m, 4H, OePen),
1.37e1.56 (m, 8H, OePen),
d9.02 (s, 2H, CH]N),
d8.09e8.12 (d, J ¼ 8.1 Hz, 2H,
d
d
d
d
d
d
d
0.93e0.97 (t, J ¼ 5.4 Hz, 6H, OePen); IR
(KBr): 2202 (C^N) cmꢁ1, 1616 (CH]N) cmꢁ1. 7b, Yield: 50.6%
(0.17 g); M.p. 210e211 ꢂC. Anal. Calcd for C42H62N6O2: C, 73.86; H,
9.15; N, 12.30. Found: C, 73.41; H, 9.46; N, 12.37. 1H NMR (300 MHz,
CDCl3):
6.34e6.37 (d, J ¼ 9.0 Hz, 2H, aromatic),
aromatic),
4.02e4.06 (t, J ¼ 6.6 Hz, 4H, OeDec),
1.71e1.81 (m, 4H, OeDec),
d
9.05 (s, 2H, CH]N),
d
8.11e8.14 (d, J ¼ 9.0 Hz, 2H, aromatic),
6.04e6.05 (d, J ¼ 2.4 Hz, 2H,
3.11 (s,12H, NMe2),
1.20e1.42 (m, 28H, OeDec), 0.85e0.90
d
d
d
d
d
d
d
(t, J ¼ 6.6 Hz, 6H, OeDec); IR (KBr): 2204 (C^N) cmꢁ1,1618 (CH]N)
cmꢁ1. 8b, Yield: 40.1% (0.13 g); M.p. 283e285 ꢂC. Anal. Calcd for
C40H42N6O2: C, 75.21; H, 6.63; N, 13.16: Found; C, 74.77; H, 6.61; N,
13.08.1H NMR (300 MHz, CDCl3):
J ¼ 9.0 Hz, 2H, aromatic),
aromatic), 6.06 (s, 2H, aromatic),
d
9.13 (s, 2H, CH]N),
7.19e7.48 (m, 10H, OeBz),
5.10e5.22 (s, 4H, OeBz),
1.06e1.20 (m, 12H, Net2); IR
d8.12e8.16 (d,
d
d6.37 (s, 2H,
d
d
d
3.32e3.39 (q, J ¼ 6.0 Hz, 8H, Net2),
d
(KBr): 2203 (C^N) cmꢁ1, 1612 (CH]N) cmꢁ1. 9b, Yield: 53.5%
(0.16 g); M.p. 310e312 ꢂC. Anal. Calcd for C38H38N6O2: C, 74.73; H,
6.27; N, 13.76: Found; C, 74.31; H, 6.24; N, 13.65. 1H NMR (300 MHz,
CDCl3):
7.33e7.40 (m, 4H, OePh),
J ¼ 8.8 Hz, 2H, aromatic),
d
8.98 (s, 2H, CH]N),
7.04e7.16 (m, 6H, OePh),
6.07 (s, 2H, aromatic),
d
8.19e8.22 (d, J ¼ 9.0 Hz, 2H, aromatic),
6.53e6.56 (d,
3.28e3.35 (q,
d
d
d
d
d
J ¼ 7.1 Hz, 8H, NEt2), 1.10e1.15 (t, J ¼ 7.1 Hz, 12H, NEt2); IR (KBr):
d
2208 (C^N) cmꢁ1, 1613 (CH]N) cmꢁ1. 10b, Yield: 72.2% (0.18 g);
M.p. 285e287 ꢂC. Anal. Calcd for C28H34N6O2: C, 69.11; H, 7.04; N,
17.27: Found; C, 69.08; H, 7.07; N, 17.26. 1H NMR (270 MHz, CDCl3):
d
8.99 (s, 2H, CH]N),
d
8.10e8.13 (d, J ¼ 9.2 Hz, 2H, aromatic),
Fig. 1. Absorption and fluorescence spectra of 1be7b (a) and 8be14b (b) in chloroform
solution. The concentration of dyes for fluorescence is ca. 1.0 ꢀ 10ꢁ5 M.
d6.32e6.36 (dd, J ¼ 7.0 and 2.2 Hz, 2H, aromatic),
d
6.03e6.04 (d,

60
B.-S. Kim et al. / Dyes and Pigments 90 (2011) 56e64
Fig. 2. Optimized molecular geometry for 1b (a) and 8b (b).
Yield: 58.9% (0.22 g); M.p.192e194 ꢂC. Anal. Calcd for C46H70N6O2: C,
and the alkyl substituents on the amino group are related by the
spacing between the adjacent 2-D stacking layers. This spacing
between the neighbouring layers is regarded as one of the important
parameters for obtaining pure J-aggregate solid films, because
J-aggregates are considered to have a low-dimensional electronic
state. Amongthe different substituents, phenylringsubstitutionwas
74.75; H, 9.55; N, 11.37: Found; C, 74.88; H, 9.59; N, 11.37. 1H NMR
(270 MHz, CDCl3):
d
9.01 (s, 2H, CH]N),
6.32e6.36 (dd, J ¼ 5.4 and 2.7 Hz, 2H, aromatic),
4.00e4.05 (t, J ¼ 5.4 Hz, 4H,
3.40e3.47 (q, J ¼ 5.4 Hz, 8H, NEt2), 1.81e1.91 (m, 4H,
0.85e0.90
d
8.09e8.13 (d, J ¼ 8.1 Hz, 2H,
aromatic),
d
d
6.03e6.04 (d, J ¼ 2.7 Hz, 2H, aromatic),
d
OeDec),
OeDec),
d
d
d1.20e1.52 (m, 40H, OeDec and NEt2), d
(t, J ¼ 5.4 Hz, 6H, OeDec); IR (KBr): 2207 (C^N) cmꢁ1, 1609
(CH]N) cmꢁ1
.
Table 1
Calculated absorption parameters for the optimized
molecular geometry.
3. Results and discussion
Dye no.
lmax/nm
1b
2b
3b
4b
5b
6b
7b
8b
397 (1.9490a)
395 (2.0438a)
393 (1.8960a)
394 (1.9010a)
393 (1.8935a)
392 (1.9075a)
393 (1.9008a)
398 (2.0132a)
398 (2.0523a)
400 (1.9488a)
400 (1.9430a)
399 (1.9462a)
399 (1.9490a)
400 (1.9499a)
Several reports on the crystal structure of bisazomethine dyes
have revealed that their crystal structure is characterized by a two-
dimensional (2-D) molecular stacking layer in which molecules are
pep stacked in a staircase arrangement with small slip angles
along the long molecular axis [26,28]. The 2-D layers are aligned
along the short molecular axis such that they form a crystal
structure. The observed 2-D molecular stacking layer feature indi-
cated that the bisazomethine dye system has the potential to form
J-aggregates and, indeed, DE2 was found to form J-aggregates in
vapour-deposited films [31], although those films were composed
of J-aggregates and a single crystalline phase.
9b
10b
11b
12b
13b
14b
With respect to the molecular arrangement along the short
molecular axis, the cyano group, the substituents on the phenyl ring,
a
Oscillator strength.

B.-S. Kim et al. / Dyes and Pigments 90 (2011) 56e64
61
examined in this study. 4-(Dimethylamino)- and 4-(diethylamino)-
2-alkoxybenzaldehydes 1ae14a were reacted with diaminomale-
onitrile to yield bisazomethine dyes 1be14b, respectively, to obtain
J-aggregates in the solid state. The active amino groups of dia-
minomaleonitrile can readily react with the aldehyde group to
afford azomethine linkages. All the prepared novel bisazomethine
dyes were obtained in yields of 40e78%.
To gain further insight into the electronic states of these bisa-
zomethine dyes, their molecular geometry and absorption charac-
teristics were computed. The optimized molecular geometry for 1b
and 8b is illustrated in Fig. 2(a) and (b), respectively. The molecule
has an almost planar
p-conjugation from the terminal amino group
to the central dicyanoethylene moiety. This molecular conformation
implies that a strong intramolecular charge-transfer exists in this
chromophoric system upon excitation. The absorption corre-
sponding to the visible absorption was estimated on the basis of
configuration interactions. The calculation result is listed in Table 1.
A strong absorption was observed for all dyes whose oscillator
strengths ranged from 1.9 to 2.0. We found no significant difference
in the calculated absorption energy. This result is in good agreement
with the absorption characteristics shown in Fig. 1. The major
component of this transition is the HOMOeLUMO transition. The
HOMO was found to consist of amino nitrogen atoms including
phenyl carbons and the central ethylenemoiety. The LUMO is mainly
distributed over the azomethine and dicyanoethylene moieties. The
transition dipole was found to be oriented along the long molecular
axis parallel to the direction from the amino nitrogen to its conju-
gated cyano nitrogen. This reflects exactly the conjugation of
The UVeVis absorption and fluorescence spectra of 1be7b and
8be14b in chloroform are shown in Fig. 1(a) and (b), respectively.
All the synthesized bisazomethine dyes show strong absorption
around 550 nm with a very large molar extinction coefficient of
about 120000e150000, which confirms the symmetrical strong
intramolecular charge-transfer chromophoric system of the bisa-
zomethine dye molecule [39]. All the absorption bands have a small
shoulder around 520 nm, and no significant difference was
observed in their spectral shape. Dyes 1be7b exhibit a sharp
fluorescent band around 595 nm. Dyes 8be14b also show a sharp
fluorescent band but the spectral region is slightly shifted to the
long-wavelength region. Thus, these derivatives can be used as
a fluorescent material for a red emitter, although their quantum
efficiency is very low. All the dyes showed a Stokes shift of about
45 nm. These experimental data clearly indicate that the substitu-
tion in the amino groups as well as in the alkoxy groups on the
phenyl ring exerts no considerable influence on the electronic
states in the visible region.
peelectrons between the terminal amino donors and the central
cyano groups. A cross-conjugation through the central ethylene
moiety is also suggested and this is considered the reason for the
very large oscillator strength of these bisazomethine dyes.
Fig. 4. Absorption (a) and fluorescence (b) spectra of 8be14b in vapour-deposited
films.
Fig. 3. Absorption (a) and fluorescence (b) spectra of 1be7b in vapour-deposited films.

62
B.-S. Kim et al. / Dyes and Pigments 90 (2011) 56e64
Table 2
Absorption and fluorescence characteristics for 1be14b in solution and in solid films.
Dye no.
lmax (nm)
Dl (nm)a
3max
Fmax (nm)b,c
D
F (nm)d
SS (nm)e
FF (%)f
In CHC13
In Film
In CHCI3
In Film
1b
2b
3b
4b
5b
6b
7b
8b
546
547
546
546
546
546
547
555
550
556
556
557
555
555
455, 589
541, 593
649
ꢁ91,43
ꢁ6,46
103
77
154,700
150,000
138,000
150,000
147,500
138,000
143,700
137,800
134,800
123,000
124,300
124,500
125,900
128,500
593
591
593
593
593
593
593
601
597
601
601
601
601
601
eg
eg
73
99
78
59
63
51
eg
50
79
49
51
39
23
47
44
47
47
47
47
46
46
47
45
45
44
46
46
0.5
0.6
0.4
0.3
0.6
0.5
0.6
0.2
0.4
0.6
1.4
0.9
1.4
1.5
664
692
671
652
656
644
eg
623
612
605
604
66
59
57
440, 587
615
ꢁ75, 32
9b
65
647
680
650
652
640
624
10b
11b
12b
13b
14b
659
621
621
601
103
65
64
46
41
596
a
Dl
¼
lmax (film) ꢁ lmax (solution).
b
c
d
e
f
Fmax (solution) excited at lmax (solution) value.
Solid-state Fmax excited at lmax (film) value.
D
F ¼ Fmax (solid) ꢁ Fmax (solution).
Stokes shift, Fmax lmax in CHC13 solution.
ꢁ
Fluorescence quantum yield.
No fluorescence detected.
g
These experimental results clearly indicate that for all the
give mono-substituted azomethine dyes, which show the hyp-
sochromic absorption band. This theory was experimentally
confirmed by preparing the corresponding monoazomethine dyes
and their vapour-deposited films. These bisazomethine dyes
showed significant spectral difference in the solid state, despite
their molecules having almost similar electronic states. Therefore,
the spectral shift is correlated with the solid-state structure; the
spectral shift is considered to depend on the alkoxy substituents on
the phenyl ring.
The absorption bands for 3b, 9b, 10b, and 11b in vapour-
deposited films are illustrated in Fig. 5, along with their absorption
spectra in chloroform solution. As mentioned above, the shape of
the spectra of 3b and 10b was very similar to that of DE2 in vapour-
deposited films and their peaks around 650 nm can be ascribed to J-
aggregate formation. In addition to these two dyes, 9b and 11b
exhibited a tendency to form J-aggregates in vapour-deposited
films. In their film absorption bands, the absorption spectrum
increases very sharply around the absorption edge in the long-
wavelength region. In the solution spectrum, the bisazomethine
dyes generally exhibit a well-defined peak as well as a relatively
prepared bisazomethine dyes in a solution, there is little effect of
the substituents on the optical properties of the dyes in the visible
region. This, of course, is attributed to the small electronic effect of
the substituents on the p-conjugation of the chromophoric system.
These novel bisazomethine dyes, however, exhibit a significant
spectral change in solid films. Figs. 3 and 4 show the absorption and
fluorescent spectra of 1be7b and 8be14b, respectively, in a vapour-
deposited film. These spectral characteristics are summarized in
Table 2, along with the spectral characteristics in a chloroform
solution. The spectral shift between the solution and the films is
also listed.
The shape of the absorption bands of 3b and 10b is noteworthy.
They are characterized by a broad band over the visible region with
a sharp peak around 650 nm. The shift between the peaks of the
solution spectra and film spectra is 103 nm in the case of both dyes.
This spectral change is quite similar to that of DE2 [31], which
shows a sharp peakdthat was assigned to J-aggregatesdin the
long-wavelength region in vapour-deposited films. Thus, J-aggre-
gates are considered to form in these films; to obtain pure J-
aggregate films, the preparation conditions of the films will have to
be examined. In the case of other dyes, both band broadening and
bathochromic spectral shifts in the absorption spectra were
observed. The degree of bathochromic shift is dependent on the
alkyl chain length of the alkoxy substituents on the phenyl rings.
The methoxy group (3b and 10b) showed the largest shift in
absorption, and the spectral shift decreased with increasing chain
length in both series. The decyloxy group (7b and 14b) showed the
shortest spectral shift. The alkoxy substituents were introduced to
modulate the spacing between the 2-D stacking molecular layers.
They also have an influence on the geometry of the molecular
stacking in the 2-D layer. This observation may thus reflect some
structural variety in molecular arrangement in the solid state.
However, the dye films showed a simple fluorescence band around
620e690 nm in the solid state. The shape of the peak was slightly
different from that in the solution. There were no significant
differences in the spectral shifts for the dyes except for 1b and 8b.
Among all the dyes, 1b and 8b showed quite an unusual absorption
band with two distinct absorption maxima around 450 nm and
600 nm. A theory to explain this phenomenon was proposed:
during vacuum deposition, both dyes are thermally decomposed to
Fig. 5. Absorption spectra of 3b, 9b, 10b and 11b in vapour-deposited films, as well as
the spectra in chloroform.

B.-S. Kim et al. / Dyes and Pigments 90 (2011) 56e64
63
small Stokes shift of about 1400 cmꢁ1. This suggests that the major
absorption peak can be assigned to the 0e0 transition. In the case of
9b and 11b, the rise in the absorption edge in the longer-wave-
length region was steeper in the case of the film absorption spectra
than in the case of the solution spectra. This implies that a pure
electronic transition in the longer-wavelength region, namely,
J-aggregate absorption, is incorporated in the film absorption
spectra. Among all dyes, four dyesd3b, 9b, 10b, and 11bdwere
considered to form J-aggregates in vapour-deposited films, on the
basis of the shape of the absorption spectrum and absorption edge.
Foranexactinterpretationof these spectralchanges and toachieve
our final goal of obtaining pure J-aggregate solid films, the preparation
conditions of the films will have to be examined and the optical
properties of the dyes will have to be characterized on the basis of the
solid-state structure. Crystal structure analysis of these dyes is thus
very important and the results will be reported elsewhere.
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investigated the effect of phenyl ring substitution in bisazomethine
chromophoric systems, synthesized using diaminomaleonitrile and
aminobenzaldehydes, with alkoxy groups. In chloroform solution,
all the synthesized bisazomethine dyes exhibited almost similar
optical properties, namely, strong absorption around 550 nm and
weak red fluorescence around 590 nm. Molecular orbital calcula-
tions confirmed the strong intramolecular charge-transfer property
of the synthesized dyes and the calculation result was in good
agreement with their solution properties. In the case of vapour-
deposited films, the absorption spectra of the dyes showed a variety
of spectral changes in the visible region. Four of the synthesized
derivatives were found to form J-aggregates in vapour-deposited
films, as determined from the shape of the spectrum and the
absorption edge. Further investigation of the observed spectral
changes, which involves crystal structure analysis of all the dyes, is
underway. In addition, to obtain pure J-aggregate solid films, the
various preparation conditions of the films and other combinations
of substituents will be examined.
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Acknowledgement
This research was financially supported by the Japan Society for
the Promotion of Science (JSPS) and the Korea Science and Engi-
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Cooperation Program as well as the Sasagawa Scientific Research
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