Electro-optical properties and X-ray crystal structure of a new bisazomethine dye

Article abstract of DOI:10.1080/15421400802333352

The photoluminescence and electroluminescence properties of a new bisazomethine dye derived from diaminomaleonitrile were investigated. This dye was examined as red-light-emitting materials in organic EL devices. The crystal structure of a new bisazomethine dye has been determined by X-ray crystallography. The molecules were found to form J-aggregate-like molecular arrangement.

Full text of DOI:10.1080/15421400802333352

This article was downloaded by: [University of Tennessee, Knoxville]
On: 26 December 2014, At: 17:05
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Molecular Crystals and Liquid
Crystals
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/gmcl20
Electro-Optical Properties and
X-ray Crystal Structure of a
New Bisazomethine Dye
Young-A Son b , Shinya Matsumoto c , Eun-Mi Han d
Sheng Wang a & Sung-Hoon Kim a
,
a Department of Textile System Engineering ,
Kyungpook National University , Daegu , South Korea
b BK21 FTIT, Department of Organic Materials and
Textile System Engineering , Chungnam National
University , Daejeon , South Korea
c Department of Environmental Sciences , Faculty of
Education and Human Science, Yokohama National
University , Yokohama , Japan
d Department of Chemical Engineering , Chonnam
National University , Kwangju , South Korea
Published online: 31 Aug 2012.
To cite this article: Young-A Son , Shinya Matsumoto , Eun-Mi Han , Sheng Wang &
Sung-Hoon Kim (2008) Electro-Optical Properties and X-ray Crystal Structure of a New
Bisazomethine Dye, Molecular Crystals and Liquid Crystals, 492:1, 46/[410]-55/[419],
DOI: 10.1080/15421400802333352
To link to this article: http://dx.doi.org/10.1080/15421400802333352
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no

representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Mol. Cryst. Liq. Cryst., Vol. 492, pp. 46=[410]–55=[419], 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802333352
Electro-Optical Properties and X-ray Crystal Structure
of a New Bisazomethine Dye
Young-A Son2, Shinya Matsumoto3, Eun-Mi Han4,
Sheng Wang1, and Sung-Hoon Kim1
1Department of Textile System Engineering, Kyungpook National
University, Daegu, South Korea
2BK21 FTIT, Department of Organic Materials and Textile System
Engineering, Chungnam National University, Daejeon, South Korea
3Department of Environmental Sciences, Faculty of Education and
Human Science, Yokohama National University, Yokohama, Japan
4Department of Chemical Engineering, Chonnam National University,
Kwangju, South Korea
The photoluminescence and electroluminescence properties of a new bisazomethine
dye derived from diaminomaleonitrile were investigated. This dye was examined
as red-light-emitting materials in organic EL devices. The crystal structure of a
new bisazomethine dye has been determined by X-ray crystallography. The mole-
cules were found to form J-aggregate-like molecular arrangement.
Keywords: azomethine dye; electroluminescent (EL); emitting materials; X-ray crystal
structure
INTRODUCTION
Organic electroluminescent (EL) devices have received attention
because of potential application to full color flat panel displays. The
distinctive characteristics of organic ELs are that they utilize organic
fluorescent or phosphorescent dyes as an emitter. Therefore, they can
provide various emission colors in accordance with a wide selection of
organic fluorescent dyes [1–3]. Since Tang and VanSlyke reported that
This work was supported by Korea Science & Engineering Foundation through the
Joint Research Program (Grant No. F01-2007-000-10014-0).
Address correspondence to Sung-Hoon Kim, Department of Textile System Engi-
neering, Kyungpook National University, Daegu 702-701, South Korea. E-mail:
shokim@knu.ac.kr
46=[410]

New Bisazomethine Dye
47=[411]
a double layered organic EL device consisting of a hole injection layer
and an emitting layer exhibited a luminance over 1000 cd mꢀ2 at a
relatively low driven voltage of 10 V, those have been extensive studies
on layered organic EL devices with the aim of achieving high bright-
ness and full color emission [4–6]. Since the first discovery of the dou-
ble organic layer EL devices [4] consisting of diamine hole transport
layer and a 8-hydroxyquinoline aluminium (Alq3) complex emitting
layer in 1987, EL devices has been studied due to their practical appli-
cation as a full color flat panel displays. After Tang’s research work,
other 8-hydroxyquinoline derivatives metal complex were also used
as an emitter [7]. A bisazomethine dye derived from diaminomaleoni-
trile together with 4-diethylaminobenzaldehyde [8] has been studied
as a material for organic electroluminescent devices because of its
red fluorescence in solution as well as in the solid state [9]. Recently,
we also showed that azomethine dyes, which have bright red PL
light, are promising materials for the red-light-emitting OLED [10].
In this paper, we report on the synthesis, EL properties and X-ray
crystal structure of a new azomethine dye, in which the butoxy group
enhances the steric hindrance of the molecule, as an emitting
material.
EXPERIMENTAL
Elemental analyses were recorded on a Carlo Elba Model 1106
analyzer. Mass spectra were recorded on a Shimadzu QP-1000 spec-
trometer using electron energy of 70 eV and the direct probe EI
method. 1H NMR spectra were recorded on a Varian Unity Inova
400 MHz FT-NMR spectrometer with TMS as internal standard.
UV-visible spectra were recorded on a Shimadzu 2100 spectrometer.
Melting points were determined using an Electro-thermal IA 900
apparatus and are uncorrected. The 4-(diethylamino)-2-butoxyben-
zaldehyde 2 was synthesized according to the literature method
[11] with a high yield of 90%.
Bisazomethine Dye 4
Diaminomaleonitrile
3 (0.1 g, 0.6 mmol) and 4-(diethylamino)-2-
butoxybenzaldehyde 2 (0.3 g, 1.2 mmol) were heated at 60ꢁC for 7 h in
benzene (10 ml) containing 1 ml of piperidine. Water was removed azeo-
tropically using a Dean-Stark trap. The reaction mixture was cooled
to room temperature. The precipitated crude product was separated by
filtration, washed with methanol and recrystallized from chloroform.

48=[412]
Y.-A. Son et al.
21% yield; mp 128–130ꢁC MS m=z Mþ681; 1H NMR (400M Hz, CDCl3); d
0.98(t, J ¼ 7.04, 6H), 1.21(t, J ¼ 7, 12H), 1.34(t, J ¼ 7.04, 3H), 1.54(m,
J ¼ 7.52, 4H), 1.89(m, J ¼ 7.52, 4H), 3.40(m, J ¼ 7, 8H), 4.05(m,
J ¼ 6.52, 4H), 4.24(m, J ¼ 7, 2H), 6.14(s, 2H), 6.28(d, J ¼ 8.8, 2H),
6.59(s, 1H), 6.75(d, J ¼ 13.52, 2H), 7.33(d, J ¼ 8.8, 2H), 7.67(d,
J ¼ 7.52, 2H), 7.91(S, 1H); Anal. Cald for C42H55N3O5: C, 73.98; H,
8.13; N, 6.16. Found; C, 73.75; H, 8.39; N, 6.24.
Fabrication of EL Device
Bisazomethine dye 4 and a-NPD (N,N0-di-[(1-naphthalenyl)-N,N0-
diphenyl]-1,10-biphenyl)-4,40-diamine) were used as an emitting layer
and a hole transporting layer in EL devices. a-NPD has a high hole
drift mobility and has been utilized as a hole transport layer in organic
devices. The structure of organic EL devices was ITO=a-NPD=
Azomethine dye=Alq3=LiF=Al. In a device with Al cathode, dye, a-
NPD, LiF and Alq3 layer were deposited by vacuum thermal evapor-
ation on a ITO under a vacuum of about 2 ꢂ 10ꢀ6 Torr. LiF was used
for enhancing electron injection efficiency of OLEDs. The thickness
of a-NPD,dye, Alq3, LiF and Al cathode were about 40, 40, 20, 0.5
and 100 nm, respectively, which were measured by a quartz crystal
thickness monitor placed near the substrate. The electron-injecting
layer is tris(8-quinolinolato)aluminium complex (Alq3), which has
electron transport properties and has been used as a electron trans-
port layer in EL device. The active area of devices is 3.0 ꢂ 3.0 mm2.

New Bisazomethine Dye
49=[413]
The electrical and luminescent characteristics of EL devices were ana-
lyzed by using a source meter 2400 (Keithley) and optical power meter
1830 S (Newport). The EL spectrum and Commission Internationale
De L’Eclairage (CIE) coordinates were measured with a Spectroradi-
ometer (Minolta CS-1000).
X-ray Crystallographic Analysis
Single crystals of dye 4 were prepared by diffusion method using chloro-
form and cyclohexane as good and poor solvents, respectively. Crystal
data: C34H46N6O2, Mw ¼ 570.78, monoclinic, P21=c, Z ¼ 2, a ¼ 8.624
ꢁ
(3), b ¼ 22.712 (6), c ¼ 8.511 (2) A, b ¼ 98.34 (3) , Dcalc ¼ 1.149 g=cm3,
11646 reflections were collected, 2798 unique (Rint ¼ 0.057), 690
observed (I > 2r(I)), 213 parameters, R1 ¼ 0.054, wR2 ¼ 0.2012,
GOF ¼ 1.002, refinement on F2. The data was collected on a Rigaku
˚
RAXIS RAPID imaging plate diffractometer with
a graphite-
monochromated CuKa radiation (40 kV, 50 mA) to a maximum 2h value
of 136.5ꢁ at room temperature. A total of 24 (Du ¼ 30ꢁ) images were
measured using an oscillation technique. An absorption correction
was applied. The structure was solved by the direct method (SIR92
[12]) and refined by least-squares calculations using the Crystal
Structure software package [13]. All non-hydrogen atoms were refined
anisotropically. All hydrogen atoms were placed on the calculated posi-
tions and refined by riding model.
RESULTS AND DISCUSSION
It is well known that the amino groups of diaminomaleonitrile 3 react
with carbonyl groups to afford azomethine linkages. The condensation
of compound 3 with arylaldehydes proceeded in the presence of piperi-
dine in benzene, removing the generated water with Dean-Stark trap.
We studied OLED using theazomethine dye 4. Figure 1 shows the
configuration of EL device fabricated in the present study and the
structure of a-NPD. Recently, a thin layer of inorganic Li compounds,
such as Li2O and LiF, was reported to be useful in bilayer cathode sys-
tems. This cathode system is based on the assumption that the organic
layer at the cathode interface is doped with a low-work-function metal,
such as Li, when such a reactive metal is evaporated onto the organic
layer. As a result, the barrier height for electron injection from the
cathode to the organic layer is lowered. Comparison of the absorption
spectra in solution and vapor deposited thin film of dye is illustrated in
Figure 2.

50=[414]
Y.-A. Son et al.
FIGURE 1 Device configuration of EL and molecular structure of a-NPD.
The kmax of dye 4 was caused due to intramolecular charge transfer
chromophore system in which the arylamine moiety is a donor and the
central ethylene moiety is an acceptor. Dye 4 absorbed at 555 nm in
chloroform, but the absorption maximum was found to shift to the
longer wavelength in vapor deposited thin films. The fluorescence
spectra also exhibit a bathochromic spectral shift. These bathochromic
shifts would be caused by intermolecular interactions in the solid
state.
Figure 3 shows the characteristics of applied voltage-current den-
sity of EL device with dye 4. Turn-on voltage of the OLED with dye
1 is about 20 V. The current density of dye has 15 mA=cm2 at 30 V.
Red light emission was observed for the EL device under forward bias.
Figure 4 shows the voltage-luminescence (V-L) characteristics of the
EL devices. The luminescence intensity was exponentially increased
with increasing voltage in dye 4. The linear dependence of the lumi-
nescence intensity on the voltage is indicated that charge carriers
are easily injected from both the electrodes by increasing the voltage
or current density. The device with dyeshowed a maximum luminance
of 24 cd=m2 at a current density of 18 mA=cm2 at 30 V. The light emit-
ting property was confirmed from EL device. But the corresponding

New Bisazomethine Dye
51=[415]
FIGURE 2 UV-vis (a) and photoluminescence (b) spectra of dye 4 in chloro-
form and in vapor deposited thin films.
luminescence and emitting efficiencies are not sufficient to use in
practical purposes. Figure 5 shows the EL spectra of the device. EL
spectra for the devices show a main peak at approximately 680 nm.

52=[416]
Y.-A. Son et al.
FIGURE 3 Voltage-current (V-I) density characteristics of the EL devices
with dye 4.
The CIE coordinates are x ¼ 0.68, y ¼ 0.29 which correspond to the red
emission.
X-ray structural analysis indicated another important charac-
teristic of dye 4. The molecule was found to have an almost planar
FIGURE 4 Voltage-luminescence (V-L) characteristics of EL device.

New Bisazomethine Dye
53=[417]
FIGURE 5 Electroluminescence (EL) spectra of the multilayer EL device.
conjugated system with trans conformation. As shown in Figure 6,
molecules are arranged in a characteristic fashion which is remi-
niscent of the proposed molecular arrangement for J-aggregates
[14–16]. Figure 6(a) depicts a two-dimensional stacking column on
the ac plane. In this column, molecules are stacked along the (102)
direction with the slip angles of about 16 and 24ꢁ with respect to
the long molecular axis. This molecular arrangement is very similar
to the ‘‘brick-stone’’ structure, which is one of the well-known struc-
ture for J-aggregates. These stacking columns are aligned along the
b-axis by twofold screw symmetry to give three-dimensional crystal
structure. Molecules were also found to form a two-dimensional mol-
ecular layer on the (102) plane through these stacking columns as
shown in Figure 6(b). The ‘‘brick-stone’’ structure is also recognized
in this layer, even though the molecules are not completely parallel.
These characteristic molecular arrangements are considered to con-
tribute to the observed bathochromic shift in both absorption and flu-
orescent spectra from solution to the solid state.
Bisazomethine dyes based on daminomaleonitrile are known to
form characteristic J-aggregate-like molecular arrangements in single
crystals [17,18] and several derivatives form J-aggregates in vacuum-
deposited films [19,20]. The present X-ray analysis is thus considered
to reveal the potential of dye 4 to form J-aggregates in an appropriate
medium or in the solid state.

54=[418]
Y.-A. Son et al.
FIGURE 6 (a) Two-dimensional molecular stacking column on the ac plane
and (b) two-dimensional molecular layer on the (102) plane.
REFERENCES
[1] Tokailin, H., Matsuura, M., Higashi, H., Kosokawa, C., & Kusumoto, T. (1993).
Proc. SPIE, 38, 1901.
[2] Wakimoto, T., Yonemoto, Y., Funaki, J., Tsuchiya, M., Murayama, R., & Nakada,
H. (1997). Synthetic Metals, 15, 91.
[3] Kido, J., Shinoya, H., & Nagai, K. (1995). Appl. Phys. Lette., 67, 2281.
[4] Tang, C. W. & VanSlyke, S. A. (1987). Appl. Phys. Lett., 51, 913.
[5] Adachi, C., Tokito, S., Tsutsui, T., & Saito, S. (1998). Jpn. J. Appl. Phys., 27, L269.
[6] Tang, C. W., VanSlyke, S. A., & Chen, C. H. (1989). J. Appl. Phys., 65, 3610.
[7] Hamada, Y., Sano, T., Fujita, T., Nishino, Y., & Shibata, K. (1993). Jpn. J. Appl.
Phys., 32, L514.

New Bisazomethine Dye
55=[419]
[8] Begland, R. W. (1976). US Patent 3962220.
[9] Shirai, K., Matsuoka, M., & Fukunishi, K. (2000). Dyes and Pigments, 47, 107.
[10] Kim, S. H., Yoon, S. H., Kim, S. H., & Han, E. M. (2005). Dyes and Pigments, 64, 45.
[11] Jung, B. J., Lee, J. I., Chu, H. Y., Do, L. M., Lee, J., & Shim, H. K. (2005). J. Mater.
Chem., 15, 2470.
[12] SIR92: Altomare, A., Burla, M. C., Camalli, M., Cascarano, M., Giacovazzo, C.,
Guagliardi, A., & Polidori, G. (1994). J. Appl. Cryst., 27, 435.
[13] Crystal Structure 3.8: Crystal Structure Analysis Package, Rigaku and
Rigaku=MSC (2000–2007). 9009 New Trails Dr. The Woodlands TX 77381 USA.
¨
[14] Czikklely, V., Forsterling, H. D., & Kuhn, H. (1970). Chem. Phys. Lett., 6, 11–14.
[15] Smith, D. L. (1974). Photogr. Sci. Eng., 18, 309–322.
[16] Nakatsu, K., Yoshioka, H., & Nishigaki, S. (1983). Nihon Shashin Gakkai-shi (in
Japanese), 46, 89–98.
[17] Matsumoto, S., Shirai, K., Kobayashi, K., Wada, T.,
&
Shiro, M. (2004).
Z. Kristallogr., 219, 239–243.
[18] Kim, S. H. & Matsumoto, S. (2007). Dyes and Pigments, 72, 406–408m.
[19] Matsumoto, S., Kobayashi, T., Aoyama, T., & Wada, T. (2003). Chem. Commun.,
1910–1911.
[20] Matsumoto, S., Satoh, M., Tsuchida, D., Kobayashi, T., Aoyama, T., & Wada, T.
(2005). Trans. MRS-J, 30, 345–348.