Spectroscopic investigation of laser-induced processes in a series of azobenzene-containing side-chain polymers

We investigate the photoinduced processes in films of a series of three side-chain azobenzene-containing polymers, which differ only in the length of the spacers attaching the chromophores to the main chain. Two of them are amorphous and one is liquid-crystalline. Illumination of the polymer films with an Ar-laser beam results in changes in their absorption spectra and to the appearance of dichroism. In the polymer with shortest spacers the irradiation gives rise to a considerable photoequilibrium concentration of cis-azobenzenes resulting from the photoinduced reversible trans-cis isomerization. In the polymer with long spacers, which is liquid-crystalline, the main result from the irradiation is the reorientation of the trans-azobenzenes and the photodichroism in this film is much larger. The induced dichroism is stable in this liquid-crystalline film; it disappears with time in the amorphous films.