Photo-orientation in azobenzene containing polybutadiene based polymer

The photochemical behavior of a liquid crystalline polymer based on HO-terminated telechelic polybutadiene Krasol LBH 3000 grafted with 5-(4-{[4-(octyloxy)phenyl]azo}phenoxy)pentane-1-thiol units was studied. The photochemically induced trans-cis-trans isomerization cycles of azobenzene groups resulted in their local reorientation upon irradiation with linearly polarized UV light of He-Cd laser. The irradiation led to a reorientation of the azobenzene chromophores perpendicular to the electric field vector and in this way to the induction of stable anisotropy represented by a maximum of dichroic ratio of 5.6 at 325 nm. The resulting dichroism and birefringence was quite stable. Erasing of the orientation was carried out by the irradiation with 365 nm light of Hg-lamp. Upon irradiation with polarized and non-polarized light of the lamp, the polymer film went to a completely disordered state. Further irradiation with the linearly polarized laser beam led again to the induction of anisotropy.