Synthesis and electrooptical properties of metal-containing azopolymers. The influence of steric factors on the electro-optical effect in polycomplexes of azobenzene derivatives with cobalt

Article abstract of DOI:10.1080/15421400801926131

We propose new structures of metal-containing azopolymers with changeable electro-optical properties in consequence of different coordination metal ions. The new monomers - 4-methacroyloxy-(4'-carboxy-3'-hydroxy)-azobenzene, 4-methacroyloxy-2'-carboxy-azobenzene and their complexes with Co and polymers based of these ones are synthesized. The influence of the electric field on the absorption spectra of new metal-containing azopolymers films are investigated. Electro-optical properties of polymeric films is determined by the re-orientation of dipole moments of azobenzene groups photo induced by polarized light in the electric field. Increase of structural inflexibility by the photo isomerization of azobenzene groups decrease the electro-optical effect value.

Full text of DOI:10.1080/15421400801926131

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Synthesis and Electrooptical
Properties of Metal-Containing
Azopolymers. The Influence of
Steric Factors on the Electro-
Optical Effect in Polycomplexes
of Azobenzene Derivatives
with Cobalt
Irina Savchenko a , Nikolaj Davidenko a , Irina
Davidenko a , Anatolij Popenaka a & Vladimir
Syromyatnikov a
a Kiev National Taras Shevchenko University,
Macromolecular Chemistry Department , Ukraine
Published online: 31 Aug 2012.
To cite this article: Irina Savchenko , Nikolaj Davidenko , Irina Davidenko , Anatolij
Popenaka & Vladimir Syromyatnikov (2008) Synthesis and Electrooptical Properties of
Metal-Containing Azopolymers. The Influence of Steric Factors on the Electro-Optical
Effect in Polycomplexes of Azobenzene Derivatives with Cobalt, Molecular Crystals
and Liquid Crystals, 485:1, 1002-1010, DOI: 10.1080/15421400801926131
To link to this article: http://dx.doi.org/10.1080/15421400801926131
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Mol. Cryst. Liq. Cryst., Vol. 485, pp. 254=[1002]–262=[1010], 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400801926131
Synthesis and Electrooptical Properties of
Metal-Containing Azopolymers. The Influence of Steric
Factors on the Electro-Optical Effect in Polycomplexes
of Azobenzene Derivatives with Cobalt
Irina Savchenko, Nikolaj Davidenko, Irina Davidenko,
Anatolij Popenaka, and Vladimir Syromyatnikov
Kiev National Taras Shevchenko University, Macromolecular
Chemistry Department, Ukraine
We propose new structures of metal-containing azopolymers with changeable
electro-optical properties in consequence of different coordination metal ions. The
new monomers – 4-methacroyloxy-(40-carboxy-30-hydroxy)-azobenzene, 4-metha-
croyloxy-20-carboxy-azobenzene and their complexes with Co and polymers based
of these ones are synthesized. The influence of the electric field on the absorption
spectra of new metal-containing azopolymers films are investigated. Electro-optical
properties of polymeric films is determined by the re-orientation of dipole moments
of azobenzene groups photo induced by polarized light in the electric field. Increase
of structural inflexibility by the photo isomerization of azobenzene groups decrease
the electro-optical effect value.
Keywords: azobenzene; dipole moment; electrooptics; metallopolymers; photo isomeri-
zation; polycomplexes
1. INTRODUCTION
Azobenzene functionalized polymers are interesting because it com-
bine the properties of anisotropy with photoresponsive behavior that
give rise to applications in areas such as optical storage, optical
switching, diffractive optical elements, non-linear optical devices, LC
displays etc. [1–3].
Address correspondence to Irina Savchenko, Kiev National Taras Shevchenko
University, Macromolecular Chemistry Department, 60, Vladimirskaya Str., 01033
Kiev, Ukraine. E-mail: iras@univ.kiev.ua
254=[1002]

Electro-Optical Effect in Azobenzene Polycomplexes
255=[1003]
Under the action of linearly polarized light, which is absorbed by
azobenzene groups and leads to changes in isomeric structures,
polarization is induced in the films. The photoinduced polarization
appears under influence of linearly polarized light in polymeric films.
It can be changed by thermal or mechanical treatments in external
electric andnor magnetic fields, under light illumination. The rotation
of dipole moments occurs in the external electric field. Since the mech-
anism of the influence of electric and magnetic fields is connected with
the aligning forces for dipole moments of azobenzene groups [4–6] one
can suppose that the electro-optical effect depends on steric factors
which complicates the displacement of electric dipoles and metal ions.
It mean for the selection of substances used in optoelectronics.
The aims of this work were the synthesis of new metal-containing
azopolymers and investigation the optical and electrical properties of
their polymeric films depending on structural peculiarities of cobalt
ions coordination.
Polymer metal chelates with cobalt were synthesized.

256=[1004]
I. Savchenko et al.
The structures of the monomers and metal complexes were con-
firmed by the data of NMR- and infrared spectroscopes.
2. EXPERIMENTAL
2.1. Synthesis of Azocompounds
Synthesis of 4-hydroxy-(40-carboxy-30-hydroxy)-azobenzene
and 4-hydroxy-(20-carboxy)-azobenzene
4-amino-2-hydroxybenzoic acid (0.1 mol) or 2-aminobenzoic acid
(0.1 mol) was dissolved in a solution of concentrated 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 mol) 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 mol) in NaOH solution (100 mL)
was added slowly. The resulted solution was stirred for 4 h at 0–5ꢀC
and for an additional 10 h at room temperature. The precipitate
formed was collected by vacuum filtration 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-(20-carboxy)-azobenzene
1H NMR (400 MHz, DMSO, d, ppm): 7.79-6.90 (2d, m, 8H, Ph-H),
11.0 (s, 1H, COOH), 10.14 (s, 1H, OH).

Electro-Optical Effect in Azobenzene Polycomplexes
257=[1005]
2.2. Synthesis of Monomers
The synthetic route for the target monomers is shown by Schemes 1, 2.
The synthesis of 4-methacroyloxy-(40-carboxy-30-hydroxy)-azoben-
zene, as an example, is given below: azocompound (2.58 g, 0.01 mol)
was dissolved in 25 mL anhydrous THF, and freshly distilled triethy-
lamine (1.53 mL, 0.011 mol) was added to the solution. The reaction
mixture was then cooled to 0–5ꢀC. Methacryloyl chloride (1.07 mL,
0.011 mol) in THF (5 mL) was injected gradually 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. 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, C-CH3).
SCHEME 1 Synthesis of 4-methacroyloxy-(40-carboxy-30-hydroxy)-azobenzene.
SCHEME 2 Synthesis of 4-methacroyloxy-(20-carboxy)-azobenzene.

258=[1006]
I. Savchenko et al.
4-Methacroyloxy-(20-carboxy)-azobenzene
1H NMR (400 MHz, DMSO, d, ppm): 8.08–6.9 (2d, m, 8H , Ph-H),
=
=
11.0 (s, 1H, COOH), 6.34 (s, 1H C CH2, cis), 5.87 (s, 1H C CH2, trans),
=
2.06 (s, 3H, C-CH3).
2.3. Synthesis of Chelates
New complexes of 4-methacroyloxy-(40-carboxy-30-hydroxy)-azoben-
zene and 4-methacroyloxy-(20-carboxy)-azobenzene with Co were
synthesized by the exchange reaction between acetates of the corre-
sponding metal (0.001 mol) and monomers (0.002 mol) in alcohol-
NaOH solution (20 mL) and purified by recrystallization from ethanol.
The structures of the obtained complexes of 4-methacroyloxy-(40-
carboxy-30-hydroxy)-azobenzene and 4-methacroyloxy-(20-carboxy)-
azobenzene with Co 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 10 wt.% DMF solution of mono-
mer with AIBN as free radical initiator (10 wt.% with respect of mono-
mer mass) at 80ꢀC for more than 30 hours in thermostat. The
polymerization mixture was poured into methanol. The solid precipi-
tate was filtered, dissolved in DMF, and reprecipitated into methanol
and then dried at 20ꢀC overnight.
The synthesized polycomlexes were characterized by 1H NMR spec-
troscopy. 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
TABLE 1 Some Distinctive Absorption Bands of Metallic Complexes of
4-methacroyloxy-(40-carboxy-30-hydroxy)-azobenzene (I) and
4-methacroyloxy-(20-carboxy)-azobenzene (II)
CoL2
nas (COOꢁ)
ns (COOꢁ)
n (COC)
n (C¼O)
I
II
1600
1590
1380
1370
1140
1135
1715
1720

Electro-Optical Effect in Azobenzene Polycomplexes
259=[1007]
investigations. The thickness of the polymeric films was 1–2 mg.
These samples were used for the following measurements: the spectra
of optical density D of the polymeric films over the range of light wave-
length k ¼ 350–900 nm; the value IE=I0, where I0 and IE are the mono-
chromatic light intensities respectively before and after application of
the electric field. Nonpolarized and polarized light was used for illumi-
nation of the samples. In the latter case the sample was located
between two polarizers at an angle of ninety degrees. The electric field
(E ¼ 1 ꢂ 108 V=m) was produced by the corona discharge [7]. The value
dIE was determined in dependence on time (t) of the illumination with
polarized light and after this illumination, light wavelength k, angle h
between directions of polarized axes of the polarizer and analyzer. All
experiments carried out at room temperature T ¼ 293 K, the influence
of depolarization properties of the layer SnO2:In2O3 [8] is graded.
3. RESULTS AND DISCUSSION
The absorption spectra of the investigated polymeric films are shown
on Figure 1. The absorption is determined by light excitation of
azobenzene groups and it is not sensitive on the presence of metallic
ions in polymers. The electric field had a more appreciable effect on
FIGURE 1 Spectra of optical density (D) and dependences of dIE of k of the
polymeric films A1 (1, 10), A1-Co (2, 20), A2 (3, 30), A2-Co (4, 40) measured for
h ¼ p=2 after their illumination by linearly polarized light (k < 500 nm) during
60 min.

260=[1008]
I. Savchenko et al.
the light transmission when the samples were pre irradiated by polar-
ized light in the absorption range of azobenzene groups (k < 550 nm).
The most significant change in I0 induced by an external electric field
is observed after exposure of the samples to light transmitted through
the polarizer (exposure time t > 30 s) and when an analyzer with
h ¼ p=2 is used [7]. Figure 1 shows the dependences of dIE on k, mea-
sured for h ¼ p=2 after a long-term exposure of the samples by polar-
ized light with k < 550 nm. The influence of electric field on the light
transmission is increased after long-term irradiation by polarized light
in the long-wave part of the absorption range of investigated polymeric
films.
At comparison A1, A2 with A1-Co, A2Co is changed the mark of dIE
and the time constant (sE) is increased after the external electric field
is switched on and is switched off.
The kinetics of light intensity changes from I0 to IE and after the
electric field is switched off can be described by the simple correla-
tions:
IðtÞ ¼ I0 þ ðIE ꢁ I0Þð1 ꢁ expðꢁt=sEÞÞ
ð1Þ
and
IðtÞ ¼ I0 þ ðIE ꢁ I0Þ expðꢁt=sEÞ;
ð2Þ
in which time constant sE averages 60 ꢃ 10 s for A1, A1-Co, 90 ꢃ 10 s
for A2, A2-Co (Fig. 2).
FIGURE 2 Dependences of dIE on time t after switching on E and switching
off, measured for h ¼ p=2 and k ¼ 625 nm for the samples A1-Co (1), A2-Co (2)
after theirs illumination by linearly polarized light during 60 min.

Electro-Optical Effect in Azobenzene Polycomplexes
261=[1009]
The increase of sE can be explained by the influence of steric factors
at rotations of azobenzene isomers.
4. CONCLUSIONS
In our structures photoinduced optical anisotropy arises as a result of
irradiation by linearly polarized light, which causes trans-cis isomer-
ization of azobenzene groups. An external electric field orientates
the light-induced dipole moments of these groups, causing the
electro-optic effect at wavelengths near the long-wave absorption edge
of the polymers (Fig. 1).
In films A1, A2 an external electric field involves alignment of
photoinduced dipoles along the field force lines and the polarized light
interacts with these dipoles and for h ¼ p=2 the value dIE < 0. In films
A1-Co, A2-Co the polarized light is dissipated and it is depolarized in
the external electric field dIE > 0. The last one perhaps [9] is related to
the more strong interaction of Co2 þ ions with E than the interaction of
dipoles and Co2 þ ions are bonded with azobenzene fragments but the
direction of this bond does not coincide with the direction of the
photoinduced dipole moment. Consequently, the change of orientation
angle of photoinduced dipoles in the external electric field in the
samples A1-Co, A2-Co over the bond with metallic ions back in films
A1, A2.
The influence of the metallic ion in the samples A1-Co in compari-
son to A2-Co is reduced over the increase of forces of elasticity which
are prevented from the rotation of dipole moments of azobenzene
groups [9]. At comparison A1-Co with A2-Co the dIE is decreased
and the sE is increased because of steric difficulties in films A2-Co
which is determined the immediate bond Co ion with azobenzene
groups.
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