Characterization of new benz-X-azole dye derivatives and metal complexes

Article abstract of DOI:10.1080/15421400802615527

Novel luminescence dyes having benzoxazole 3 and benzthiazole 4 moieties were synthesized and characterized. Zinc (II) complex dyes 5 and 6 were consecutively prepared and their corresponding light emitting properties were also studied with respect to the

Full text of DOI:10.1080/15421400802615527

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Characterization of New Benz-
X-Azole Dye Derivatives and
Metal Complexes
Young-A Son a , Byung-Soon Kim a , Myung-Sik Choi b
& Sung-Hoon Kim b
a BK21 FTIT, Department of Organic Materials and
Textile System Engineering , Chungnam National
University , Daejeon, Korea
b Department of Textile System Engineering ,
Kyungpook National University , Daegu, South Korea
Published online: 22 Jul 2010.
To cite this article: Young-A Son , Byung-Soon Kim , Myung-Sik Choi & Sung-
Hoon Kim (2009) Characterization of New Benz-X-Azole Dye Derivatives and
Metal Complexes, Molecular Crystals and Liquid Crystals, 498:1, 158-164, DOI:
10.1080/15421400802615527
To link to this article: http://dx.doi.org/10.1080/15421400802615527
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Mol. Cryst. Liq. Cryst., Vol. 498, pp. 158–164, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802615527
Characterization of New Benz-X-Azole Dye Derivatives
and Metal Complexes
Young-A Son1, Byung-Soon Kim1, Myung-Sik Choi2,
and Sung-Hoon Kim2
1BK21 FTIT, Department of Organic Materials and Textile System
Engineering, Chungnam National University, Daejeon, Korea
2Department of Textile System Engineering, Kyungpook National
University, Daegu, South Korea
Novel luminescence dyes having benzoxazole 3 and benzthiazole 4 moieties were
synthesized and characterized. Zinc (II) complex dyes 5 and 6 were consecutively
prepared and their corresponding light emitting properties were also studied with
respect to the photoluminescence (PL) functions of the dyes 3 and 4. The strong
light emitting properties and their resulting PL spectra were observed from the
dyes 3 and 5, namely dyes having benzoxazole moieties. To expect the molecular
conformation, theoretical modeling calculation were performed to determine the
molecular interatomic distance and dihedral angle due to the limitation of single
crystal formation from polymeric dye molecules.
Keywords: conjugated polymer; dopant=matrix system; energy transfer; Horner-
Emmons condensation; light-emitting diode
INTRODUCTION
A comprehensive number of researches have been carried out to develop
the potential areas of organic photo and electroluminescence (PL, EL)
during the last decade. Especially, organic fluorescent or phosphor-
escent dyes have been used as emitting materials. Thus, these dyes
can provide various emission colors in accordance with a wide selection
of fluorescent dyes [1–4]. Generally, organic photoluminescence (PL)
This research was supported by the Program for the Training of Graduate Students
in Regional Innovation which was conducted by the Ministry of Commerce Industry and
Energy of the Korean Government.
Address correspondence to Prof. Sung-Hoon Kim, Department of Textile System
Engineering, Kyungpook National University, Sankyuk-dong, Buk-gu, Daegu 702-701,
Korea (ROK). E-mail: shokim@knu.ac.kr
158

Characterization of New Benz-X-Azole Dye Derivatives
159
and electroluminescence (EL) can be expressed as the emission of light
by organic molecules when they are exposed to photo irradiation and
electric field [1,5]. These potential organic light emitting materials have
been considered with wide application areas such as data transfer, sto-
rage and display of information and have also great potential for econ-
omic profit. In this context, it is of great importance to develop and
characterize new light emitting compounds in both of academic and
industrial interests.
In this work, two organic luminescence compounds having benzox-
azole and benzthiazole moieties and their zinc (II) metal complexes
have been synthesized and their PL spectra were determined. Using
DMol3 program, atomic distance and dihedral angle were also calcu-
lated and compared with the synthesized moiety.
EXPERIMENTAL
Synthesis
The intermediate compounds 1 and 2 were prepared by condensing
p-aminosalicylic acid, 6.52 mmole (0.998 g), with o-aminophenol and
o-aminothiophenol 6.52 mmole (0.711 g, 0.816 g) in 20 g of polypho-
sphoric acid (85% phophorus pentoxide) over three hours at 200ꢀC.
Other general procedures were followed by the indicated reference
[6]. For next step synthesis, the dyes 3 and 4 were obtained from
the prepared intermediates 1 and 2, which previously described refer-
ence [7,8]. Terephthalaldehyde (0.1 mmole, 0.013 g) and compounds 1
and 2 (0.2 mmole, 0.045 g, 0.048 g) were mixed and stirred in 5 ml
of benzene. 5 ꢁ 6 drops of piperidine was added dropwise during the
reaction. Reflux was continued for 2 days. The reaction product was
filtered using benzene and dried (dyes 3 and 4).
Dye 1, Yield: 23.03% (0.340 g); calculated for C13H10N2O2: C, 69.02; H,
4.46; N, 12.38: found; C, 69.16; H, 4.16; N, 12.81.
Dye 2, Yield: 38.84% (0.614 g); calculated for C13H10N2OS: C, 64.44; H,
4.16; N, 11.56; S, 13.23: found; C, 64.55; H, 4.03; N, 11.52; S, 12.62.
Dye 3, Yield: 34.80% (0.019 g); calculated for C34H22N4O4: C, 74.17; H,
4.03; N, 10.18: found; C, 73.69; H, 4.10; N, 9.45.
Dye 4, Yield: 33.98% (0.020 g); calculated for C34H22N4O2S2: C, 70.08;
H, 3.81; N, 9.62; S, 11.01: found; C, 70.09; H, 4.04; N, 9.18; S, 10.95.
The zinc (II) complexes of dyes 3 and 4 have been synthesized using
Zn(OCOCH3)2 in DMF. As shown in Scheme 1, they can be readily
obtained by the direct metal chelation of benz-X-azole legand. Dyes

160
Y.-A. Son et al.
SCHEME 1 Synthetic route of metal complexes.
3 and 4 (0.36 mmole, 0.198 g, 0.210 g) in 20 ml of DMF were dissolved
at 80ꢀC. Zn(OCOCH3)2 (0.18 mmole, 0.034 g) dissolved in 1.8 ml of
methanol was added and the reaction mixture was stirred at reflux
for 3 h. The mixtures were poured into methanol. The precipitate
was filtered, washed with methanol and dried at 50ꢀC (dyes 5 and 6).
Dye 5, Yield: 47.57% (0.108 g); calculated for C70H46N8O8Zn: C, 66.84;
H, 3.69; N, 8.91: found; C, 65.20; H, 3.01; N, 8.63.
Dye 6, Yield: 41.68% (0.099 g); calculated for C70H46N8O4S4Zn: C,
63.59; H, 3.51; N, 8.47; S, 9.70: found; C, 63.33; H, 3.19; N, 8.48;
S, 9.86.
Measurements
PL spectra were recorded with Shimadzu RF-5301 spectrofluorophot-
ometer. Elemental analyses were recorded with a Carlo Elba Model
1106 analyzer. Themogravimetric analysis (TGA) was determined by
TGA-2050 at heating 20ꢀC=min.

Characterization of New Benz-X-Azole Dye Derivatives
161
RESULTS AND DISCUSSION
For the purposes of obtaining luminescence dye intermediates, the
reaction of carboxylic groups or relevant derivatives with aromatic
ortho bisubstituted compounds was employed to produce benz-X-azole
derivatives [6,9]. In this work, p-aminosalicylic acid and o-aminophenol
(and o-aminothiophenol) were used to produce the benz-X-azole dye
intermediates as described above. After this reaction, the prepared
benz-X-azole dye intermediates 1 and 2 were reacted with dialdehyde,
namely terephthalaldehyde to produce the dyes 3 and 4. It is well
known that the active amine groups can readily react with carbonyl
groups, especially an aldehyde. For the light-emitting properties of
the dyes, benzoxazole derivative 3 showed the photoluminescent pro-
perty with solid states. In contrast, the dye 4, benzthiazole derivative
displayed lower level of photholuminescence effect (Fig. 1). Figure 1
shows the corresponding PL spectra of the benzoxazole and benzothia-
zole dye compounds. Strong emission with an emission peak around
500 nm and 540nm was observed by dye 3.
The zinc (II) complex dyes 5 and 6 were consecutively synthesized.
As shown in the PL spectra result of the dye 3 (Fig. 1), the zinc (II)
complex of the benzoxazole derivative compound (dye 5) also showed
its strong PL spectral property (Fig. 2). However, in the case of the
benzthiazole zinc (II) complex dye 6, the photoluminescence effect
was weakly observed (Fig. 2). For further molecular structural study,
FIGURE 1 PL spectra of dye 3 and dye 4 in solid state.

162
Y.-A. Son et al.
FIGURE 2 PL spectra of dye 5 and dye 6 in solid state.
FIGURE 3 Optimized molecular conformation using DMol3 modeling
calculation.

Characterization of New Benz-X-Azole Dye Derivatives
163
modeling calculation was considered to calculate the conformational
data of dyes. In general, unfortunately, organic polymeric dyes such
as dyes 5 and 6, do not readily provide the single crystals for X-ray
structural determinations, which has severely limited to obtaining
data available for exact structural characteristic studies. Thus, these
theoretical calculations were performed using DMol3 program in the
Materials Studio 4.2 package [10,11] which was the quantum mechan-
ical code using density functional theory and was then used for
spectroscopic calculations. Perdew-Burke-Ernzerhof (PBE) function
of generalized gradient approximation (GGA) level [12] with double
numeric polarization basis set [10] was used to calculate the energy
level of the frontier molecular orbital. The corresponding optimized
molecular structure of dye 5 is shown in Figure 3. The interatomic
˚
distances between Zn and the oxazole N are 2.672 and 3.664 A. The
calculated dihedral angle between two benzoxazole ligands is 104ꢀ
for dye 5. In stead of X-ray single crystal spectroscopy, the general
structural conformation of this polymeric dye molecule can be
expected using molecular modeling approaches.
In addition, thermal stabilities of the synthesized dyes were evalu-
ated by TGA using the initial degradation temperature in the tempera-
ture range of 50–800ꢀC (Fig. 4). It was determined that the synthesized
FIGURE 4 Thermal analysis for the dyes 3–6 by TGA.

164
Y.-A. Son et al.
four luminescence dyes were very stable at the temperature below
300ꢀC. This finding indicates that these dyes may provide perfect
thermostabiliy functions for the corresponding EL display end uses.
CONCLUSIONS
In this context, the benzoxazole dye type showing strong light emitting
function can be useful for the electroluminescence (EL) materials. In
addition, because the dyes 5 and 6 have two metal complex legands
in the structures, these dyes can be further coordinated to zinc to
form bridged multinuclear polymeric metal complexes. The emission
maximum of metal complex benzoxazole dye 5 is shifted from
500 nm=540 nm (dye 3) to 565 nm. This is due to the change in the dis-
tribution of electron density that occurs when the proton of the
hydroxyl group of dye 3 is removed and the remaining oxygen anion
is coordinated to metal zinc ion. In this context, since changing the dis-
tribution of the electronic density in the dye molecules affects the
energy of light emitted by the molecule, it would be possible to synthe-
size or modify EL materials that emit light of the desired wavelength.
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