Liquid-crystalline polymers bearing phenylene(azobenzene) moieties substituted with an electron-donor or electron-acceptor lateral group. Synthesis, mesomorphic behavior and photo-induced isomerization

Methacrylic polymers bearing phenylene(azobenzene) moieties substituted with a OCH3 (electron-donor) or a CN (electron-acceptor) lateral group were synthesized and their liquid-crystalline (LC) and photo-induced isomerization properties were studied. The thermotropic LC properties were analyzed by DSC, POM, and XRD. All polymers showed a mesomorphic behavior that extends over wide temperature ranges (>100 °C) displaying smectic type mesophases. The effect of the lateral group was reflected in the packing of mesogens in the smectic phases; the polar interactions of the CN groups seem to counterbalance the hindering effects of this lateral group. On the other hand, the photoisomerization of all polymers was induced in dilute solution and films (spin coated and casted). All polymers photoisomerize relatively fast with the CN-substituted polymers reaching high cis-isomer contents (>95%) at the photostationary state. Light induced birefringence experiments indicated a tight interplay between the photo-induced orientation and the LC intrinsic order. Homogeneous sinusoidal surface relief gratings were obtained.