New Azobenzene Chromophores as Monomers for Synthesis of Polyesters

Abstract

ABSTRACT:Two new azo-chromophores: 2,4-dihydroxy-4 -nitroazobenzene and 2,4-dihydroxy-4-azo-(4 -nitroazobenzeno)benzene have been prepared. These diols have been applied as monomers for polyesters synthesized in condensation with diacid chlorides: isophthaloyl chloride and sebacoyl chloride. The copolymers consist of mixture of two new diols and chlorides have been obtained as well. The polymers were identified by infrared and elemental analysis. Character of polymers was determined using X-ray spectroscopy. Thermal properties of polyesters such as glass transition temperature and thermal stability were investigated using differential scanning calorimetry (DSC) method and thermogravimetric analysis. These polymers with azobenzene groups could find potential applications as holographic recording materials. The preliminary investigations of optical grating recording were carried out.KEY WORDS Polyesters / Chromophores / Azo Dye / Photoisomerization / Holographic Recording / Azobenzene containing polymers are of special interests with respect to the reversibility of the photorearrangement, a number of interesting effects and potential applications. Such polymers in the form of solid films have been investigated for potential technological applications. It is intension to use this kind of polymers in such applications as optical information storage, optical information processing, aligning layers for liquid crystals, optical switching devices and diffractive optical elements among others. 1 The use of polymeric materials for optical applications offers many advantages in comparison with the use of inorganic materials, among them being the low weight of the optical components, the good mechanical properties of polymers, and the ease of manufacturing technical parts. 2 Many of optical applications are possible due to efficient photoisomerization and photoinduced processes such as photo-induced orientation resulting in anisotropic films or in light induced diffusion generating surface relief gratings (Scheme 1).Azobenzene groups are known to exist in two isomeric states, a thermodynamically stable trans and a meta-stable cis form. When irradiated with light of appropriate wavelength, the azobenzene chromophores undergo a reversible trans ⇒ cis ⇒ trans photoisomerization process. Linearly polarized light causes a cooperative-orientation of the azobenzene moieties and other segments of the polymers perpendicular to the electric field vector of the incident light. This results in the induction of anisotropy in the films causing a birefringence and dichroism. 1 This process can be used to Scheme 1. Photoisomerization of azobenzene groups upon linearly polarized light and photoorientation.generate erasable holographic gratings in the volume. On continued exposure the light driven diffusion process causes the formation of surface relief gratings in the same type of polymers.So the amorphous azobenzene-containing polymers are able to reversibly store optical information. Holography is a technique for memorizing the amplitude ...

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