Photochromism and holographic grating recording on a chiral side-chain liquid crystalline copolymer containing azobenzene chromophores

Polymer liquid crystals show a strong potential as optical information recording media. Recently there has been synthesized a liquid crystalline copolymer SK8 which manifests a very interesting combination of a conventional smectic A* phase and another, optically isotropic smectic phase with the transition between them (on cooling) controlled by light. Here, a detailed study of spectroscopic features and photochromism of the same copolymer has been carried out in dilute solutions and in films of different thickness. Furthermore, holographic gratings were recorded with Ar laser beams of various polarizations and their diffraction efficiency has been measured in order to estimate the technological prospects of the material. Quite unexpectedly, in the course of the work it has been found that cis-isomers in this system have a very long life time which allows preparation of the cis-form cast films directly from the UV irradiated solution. We have also observed a UV light driven phase transition at room temperature from the spontaneously formed scattering smectic A phase into the transparent TGBA* phase. A mechanism of the photo-induced transformations in this system is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.