Synthesis and electrooptical properties of metal-containing azopolymers

Article abstract of DOI:10.1080/15421400701230014

We propose new structures of polymeric composites with changeable optical characteristics (transmission and/or reflection of polarized light) under the influence of magnetic and/or electric fields. The new monomers 4-methacroyloxy-(4'-carboxy-3'-hydroxy)-

Full text of DOI:10.1080/15421400701230014

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Synthesis and Electrooptical
Properties of Metal-Containing
Azopolymers
I. Savchenko a , N. Davidenko a , I. Davidenko a , A.
Popenaka a & V. Syromyatnikov a
a Macromolecular Chemistry Department , Taras
Shevchenko Kyiv National University , Kyiv, Ukraine
Published online: 22 Sep 2010.
To cite this article: I. Savchenko , N. Davidenko , I. Davidenko , A. Popenaka & V.
Syromyatnikov (2007) Synthesis and Electrooptical Properties of Metal-Containing
Azopolymers, Molecular Crystals and Liquid Crystals, 468:1, 203/[555]-213/[565], DOI:
10.1080/15421400701230014
To link to this article: http://dx.doi.org/10.1080/15421400701230014
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Mol. Cryst. Liq. Cryst., Vol. 468, pp. 203=[555]–213=[565], 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701230014
Synthesis and Electrooptical Properties
of Metal-Containing Azopolymers
I. Savchenko
N. Davidenko
I. Davidenko
A. Popenaka
V. Syromyatnikov
Macromolecular Chemistry Department, Taras Shevchenko Kyiv
National University, Kyiv, Ukraine
We propose new structures of polymeric composites with changeable optical
characteristics (transmission and=or reflection of polarized light) under the influence
ofmagneticand=orelectricfields. Thenewmonomers4-methacroyloxy-(40-carboxy-30-
hydroxy)-azobenzene, 4-methacroyloxy-(40-carboxy-30-hydroxy)-2-nitroazobenzene,
and 4-methacroyloxy-(40-carboxy-30-hydroxy)-2-diethylamino-azobenzene, their
complexes with Co, and polymers based on their base are synthesized. The
influence of the electric field on the absorption spectra of films of the new metal-
containing azopolymers is investigated. The effect of an electric field on the trans-
mission of a linearly polarized light through the films is revealed. This effect is
determined by the re-orientation of the dipole moments of azobenzene groups which
is induced by a polarized light under the action of an electric field. The increase of
the dipole moments of azobenzene groups due to the introduction of donor and
acceptor substituents reduces the influence of Co ions on the electrooptical
properties of polymeric films.
Keywords: azobenzene;
electrooptics;
metallopolymers;
photoisomerization;
polycomplexes
INTRODUCTION
Metallopolymers are new functional materials which are used for the
application of coverings from the gaseous phase (the CVD-method), as
Address correspondence to I. Savchenko, Macromolecular Chemistry Department,
Taras Shevchenko Kyiv National University, 60, Vladimirskaya Str. Kyiv, 01033
Ukraine. E-mail: iras@univ.kiev.ua
203=[555]

204=[556]
I. Savchenko et al.
effective and selective sorbents and hardeners, superconductors, and
macroinitiators of the radical polymerization. Metallopolymers as a
new generation of polymer materials are perspective for the develop-
ment of anisotropic optic systems and films for solar batteries. The
interest in these materials causes the elaboration of new methods of
synthesis of metallopolymers.
Monomeric and polymeric composites, hybrid systems, etc. have
been found to be applicable in nonlinear optics. Nevertheless,
polymers possess advantages over other systems due to their processa-
bility and other properties. The azobenzene system [1–5] exhibits
non-linear optical properties, which make it suitable for variable kinds
of applications, for example as the optical media for the registration of
optical holograms [6], in xerography [7], etc.
The photoinduced polarization appears under the influence of a
linearly polarized light in polymeric films. It can be changed by a
thermal or mechanical treatment in external electric andnor magnetic
fields under the light illumination. In the external electric field,
the rotation of dipole moments occurs. Since the mechanism of the
influence of electric and magnetic fields is connected with the orienta-
tional forces for the dipole moments of azobenzene groups, one can
suppose that electrooptical properties should be observed in polymers
with azogroups and metallic ions chemically bound with a polymeric
chain.
The aims of this work were the synthesis of new metal-contaning
azopolymers and the investigation of the optical properties of their
films. The dependence of these properties on metal ions and sub-
stituents of the different nature in azobenzene fragments will also
be studied.
Since the newly synthesized macrochelates have two parts, i.e. the
azochromophore and a chelating group which ‘‘fasten’’ the metal in
each polymer unit, they are expected to combine two functions. Under
the influence of a polarized light, they exhibit anisotropic properties,
and, under the influence of an external electromagnetic field, they
modify electric and magnetic properties.
New polymer metal chelates with metals (Co, Ni) were synthesized.

Synthesis and Electrooptical Properties
205=[557]
The structures of the monomers and metal complexes were
confirmed by the data of NMR- and infrared spectroscopies.
EXPERIMENTAL
2.1. Monomer Synthesis
Synthesis of 4-hydroxy-(40-carboxy-30-hydroxy)-azobenzene,
4-hydroxy-(40-carboxy-30-hydroxy)-2-nitroazobenzene, 4-hydroxy-
(40-carboxy-30-hydroxy)-2-diethylaminoazo-benzene. 4-amino-2-

206=[558]
I. Savchenko et al.
hydroxybenzoic acid (15.3 g, 0.1 mol) was dissolved in a solution of con-
centrated hydrochloric acid:water (50:50) (100 ml). The mixture was
cooled to 0ꢀC in an ice-water bath, and then sodium nitrite (6.8 g,
0.1 M) was dissolved in a small amount of water added dropwise.
The reaction mixture was stirred for 2 h, and then phenol (9.4 g,
0.1 M) in a NaOH solution (100 ml) was added slowly. The resulted sol-
ution was stirred for 4 h at 0–5ꢀC and for an additional 10 h at room
temperature. The precipitate formed was collected by vacuum fil-
tration and finally dried. The product was purified by recrystallization
from ethanol. Yield: 87–92%.
4-hydroxy-(40-carboxy-30-hydroxy)-azobenzene. 1H NMR
(400 MHz, DMSO, d, ppm): 7.93–6.89 (3d, s, 7H, Ph-H), 11.4 (s, 1H,
COOH), 10.19 (s, 1H, OH).
4-hydroxy-(40-carboxy-30-hydroxy)-2-nitroazobenzene. 1H
NMR (400 MHz, DMSO, d, ppm): 7.94–6.92 (2d, 2s, 6H, Ph-H), 11.37 (s,
1H, COOH), 10.24 (s, 1H, OH).
4-hydroxy-(40-carboxy-30-hydroxy)-2-dimethylaminoazoben-
zene. 1H NMR (400 MHz, DMSO, d, ppm): 7.84–5.92 (2d, s, 6H, Ph-H),
1.24 (s, 6H, 2CH3), 3.51 (m, 4H, 2CH2), 14.75 (s, 1H, COOH), 11.41 (s,
1H, OH).
The synthetic route for target monomers is shown in Scheme 1.
2.2. Synthesis of Monomers
The synthesis of 4-methacroyloxy-(40-carboxy-30-hydroxy)-azobenzene,
as an example, is given below: the azocompound (2.58 g, 0.01 M) was
dissolved in 25 mL of anhydrous THF, and freshly distilled triethyla-
mine (1.53 mL, 0.011 M) was added to the solution. The reaction
mixture was then cooled to 0–5ꢀC. Methacryloyl chloride (1.07 mL,
0.011 M) in THF (5 mL) was gradually injected to the above solution
via a glass syringe, while the solution temperature was kept below
5ꢀC. The reaction mixture was stirred overnight at room temperature.
SCHEME 1

Synthesis and Electrooptical Properties
207=[559]
The resulting precipitate was filtered off. Purification was followed by
recrystallization from methanol. Yield: 63–76%.
4-methacroyloxy-(40-carboxy-30-hydroxy)-azobenzene.
1H
NMR (400 MHz, DMSO, d, ppm): 8.12–6.92 (3d, s, 7H, Ph-H), 11.3 (s,
=
=
1H, COOH), 6.28 (s, 1H C CH2, cis), 5.82 (s, 1H C CH2, trans), 2.06
=
(s, 3H, CꢁCH3).
4-methacroyloxy-(40-carboxy-30-hydroxy)-2-nitroazobenzene.
1H NMR (400 MHz, DMSO, d, ppm): 8.13–7.02 (2d, s, 7H, Ph-H), 11.37
=
=
(s, 1H, COOH), 6.29 (s, 1H C CH2, cis), 5.83 (s, 1H C CH2, trans), 2.06
=
(s, 3H, CꢁCH3).
4-methacroyloxy-(40-carboxy-30-hydroxy)-2-diethylamino-
1
azobenzene. H NMR (400 MHz, DMSO, d, ppm): 7.86–5.92 (2d, s,
7H, Ph-H), 1.24 (s, 6H, 2CH3), 3.50 (m, 4H, CH2), 14.75 (s, 1H, COOH),
=
=
=
6.28 (s, 1H C CH2, cis), 5.82 (s, 1H C CH2, trans), 2.08 (s, 3H, C-
CH3).
2.3. Synthesis of Chelates
New complexes of 4-methacroyloxy-(40-carboxy-30-hydroxy)-azoben-
zene,
4-methacroyloxy-(40-carboxy-30-hydroxy)-2-nitroazobenzene,
4-methacroyloxy-(40-carboxy-30-hydroxy)-2-dimethylaminoazobenzene
with Ni, Co, and Cu were synthesized by the exchange reaction
between acetates of the corresponding metal (0.001 M) and monomers
(0.002 M) in an alcohol-NaOH solution (20 mL) and purified by recrys-
tallization from ethanol.
The structures of the obtained complexes of 4-methacroyloxy-(40-
carboxy-30-hydroxy)-azobenzene with Ni, Co, and Cu have been
studied by infrared spectroscopy (Table 1).
2.4. Polymerization
Polymers were synthesized by free-radical polymerization in DMF.
The polymerization was carried out in a 10-wt.% DMF solution of a
monomer with AIBN as the free radical initiator (10 wt.% with respect
TABLE 1 Some Distinctive Absorption Bands of the Metallic Complexes of
4-methacroyloxy-(40-carboxy-30-hydroxy)-azobenzene
nas (COOꢁ)
ns (COOꢁ)
n (COC)
n (C O)
=
NiL2
CoL2
CuL2
1590
1600
1605
1380
1385
1385
1140
1140
1145
1715
1720
1725

208=[560]
I. Savchenko et al.
of the monomer mass) at 80ꢀC for more than 30 h in a thermostat. The
polymerization mixture was poured into methanol. The solid precipi-
tate was filtered, dissolved in DMF, reprecipitated into methanol,
and then dried at 20ꢀC overnight.
The synthesized polycomplexes were characterized by 1H NMR
spectroscopy. The obtained results were in agreement with the
proposed structures.
2.5. Spectral Measurements
Samples with free surface (glass substrate–conducting layer SnO2:In2O3–
polymeric film) were prepared and used in our investigations. The thick-
ness of the polymeric films was 1–2 mm. These samples were used for the
following measurements: the spectra of the optical density D of polymeric
films over the range of light wavelengths k ¼ 350–900 nm; the value IE=I0
where I0 and IE are, respectively, the monochromatic light intensities
before and after the application of the electric field. Nonpolarized and
polarized light was used for the illumination of samples. In the latter case,
the sample was located between two polarizers at an angle of ninety
degrees. The electric field (E ¼ 1ꢂ 108 V=m) was produced by the corona
discharge. The value IE=I0 was determined as a function of the illumi-
nation duration (t) by a polarized light and, after this illumination, a
function of the light wavelength k.
RESULTS AND DISCUSSION
The absorption spectra of the investigated polymeric films are shown
in Figure 1. The absorption is determined by the excitation of
azobenzene groups by light and it is not sensitive to the presence of
metallic ions in polymers. The bathochromic shift of the absorption
band at the transfer from A1, A1-Co to A2, A2-Co and A3, A3-Co is
connected with the influence of donor and acceptor substituents in
chromophore which are able to reduce of the excited state energy of
organic dyes [8].
The intensity of a nonpolarized light, which passed through the
sample after the switching-on of the electric field, has decreased
(Fig. 2) and has restored the original value after the switching-off of
the electric field (Fig. 3).
The kinetics of the light intensity changes from I0 to IE and, after
the switching-off of the electric field can be described by the relations
IðtÞ ¼ I0 þ ðIE ꢁ I0Þð1 ꢁ expðꢁt=sEÞÞ
ð1Þ

Synthesis and Electrooptical Properties
209=[561]
FIGURE 1 Spectra of the optical density (D) of polymeric films A1 (1), A1-Co
(2), A2 (3), A2-Co (4), A3 (5), A3-Co (6).
and
IðtÞ ¼ I0 þ ðIE ꢁ I0Þ expðꢁt=sEÞÞ;
ð2Þ
in which the time constant sE amounts to 60 ꢃ 10 s for A1, A1-Co,
90 ꢃ 10 s for A2, A2-Co, and 150 ꢃ 10 s for A3, A3-Co. The influence
of the electric field increases in the row A1, A1-Co; A2, A2-Co; A3,
A3-Co, decreases with increase in k, and is not observed for
k > 560 nm.
FIGURE 2 Dependences of IE=I0 for films A1 (1), A1-Co (2), A2 (3), A2-Co (4),
A3 (5), A3-Co (6) under a nonpolarized light.

210=[562]
I. Savchenko et al.
FIGURE 3 Dependences of IE=I0 on time t after the switching-on of E and the
switching-off (the moment of the switching-on of the electric field is indicated
by a vertical indicator) measured for k ¼ 544 nm for samples A1 (1), A1-Co (2),
A2 (3), A2-Co (4), A3 (5), A3-Co (6) after their illumination by a linearly polar-
ized light during 60 min.
The influence of E on the light transmission comes into a particular
prominence if samples are preliminarily illuminated by a polarized
light (at k < 550 nm which is the absorption range of azobenzene
groups). The most considerable changes of I0 at the switching-on of
the electric field are observed after the illumination of samples by
the light which passed through a polarizer during the time t > 30 s.
In Figure 4, we show the dependence IE=I0 on k which were measured

Synthesis and Electrooptical Properties
211=[563]
FIGURE 4 Dependences IE=I0 on k measured in samples A1 (1), A1-Co (2), A2
(3), A2-Co (4), A3 (5), A3-Co (6) after their illumination by a linearly polarized
light during 60 min.
after a long period of the illumination of samples by a polarized light
with k < 550 nm.
The comparison of the curves in Figures 1–4 shows that the influ-
ence of the electric field on the light transmission after the long illumi-
nation by a polarized light was intensified in the long-wave band of
absorption of the investigated compounds. The photoinduced optical
anisotropy appears as a result of the illumination of the investigated
samples by a linearly polarized light due to the trans-cis-isomerization
of azobenzene groups. The electric field orients the photoinduced dipole
moments of these groups and results in a rise of the electrooptical effect
in the long-wave range of absorption of the investigated polymers.
The influence of E on the absorption of films even without prelimi-
nary illumination of samples by a linearly polarized light (Fig. 2) is
related to the re-orientation of the dipole moments of azobenzene
groups. The larger value of sE for samples A3 and A3-Co in comparison
to that for A2, A2-Co, and A1, A1-Co testifies that the re-orientation
of the dipole moments of azobenzene groups A3, A3-Co, and A2,
A2-Co occurs slowly over steric barriers which were caused by side
substituents.

212=[564]
I. Savchenko et al.
CONCLUSIONS
The mechanism of the electrooptical effect for samples which were pre-
viously illuminated by a linearly polarized light is connected with the
appearance and accumulation of the photoinduced dipole moments of
the isomers of azobenzene groups. Since the absorption spectra of
photoinduced isomers were displaced bathochromically relative to
the absorption spectra of balanced azobenzene isomers [1,5], the
maximum influence of the electric field was observed in the visible
light range on the long-wave band of the absorption of azobenzene
groups (Fig. 4).
Photoinduced dipole moments are re-oriented in an electric field
relative to the electric vector of the exciting light wave, which results
in a change of the optical anisotropy of the investigated films. In films
A1, A2, and A2-Co, an external electric field involves the alignment of
photoinduced dipoles along the field force lines, and the polarized light
interacts with these dipoles. For h ¼ p=2, IE=I0 < 1. In film A1-Co, the
polarized light is dissipated, and it is depolarized in the external elec-
tric field IE=I0 > 1. The last fact is related, perhaps, to a stronger inter-
action of Co2þ ions with E than the interaction of dipoles. Co2þ ions are
bound with azobenzene fragments, but the direction of these bond does
not coincide with the direction of a photoinduced dipole moment. The
influence of the metallic ion in samples A2-Co and A3-Co in comparison
to A1-Co is reduced under the increase of the dipole moment of an azo-
benzene group, and the re-orientation of this dipole moment at the
external electric field prevails over the displacement of a Co2þ ion.
Thus, the effect of the influence of an external electric field on the light
transmission in the investigated films is related to the displacement of
azobenzene groups and metallic ions from their balanced location due
to the action of an external electric field. The increase of the dipole
moment of azobenzene groups, for example, by the introduction of a
donor or acceptor substituent enhances this effect and decreases the
influence of metallic ions on the re-orientation of dipole moments.
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