THERMOTROPIC AND SOLUTION PHOTOISOMERIZATION PROPERTIES OF SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS CONTAINING METHYL-SUBSTITUTED AZOBENZENE MESOGENS

The thermotropic and solution photoisomerization properties of a class of polyacrylates containing differently methyl-substituted azobenzene groups are presented. Methyl-substitution inhibits the tendency to crystallize and causes a dramatic decrease in the stability of the established nematic phases. These effects result from a restriction of the packing capability of the mesogenic groups and a reduction of their length-to-breadth ratio. In dilute solution all polymeric samples undergo trans-to-cis photoisomerization of the azo group upon irradiation in the absorption region of the pi --> pi* electronic transitions. Photoisomerization rate constants are very similar and of the same order of magnitude as those observed for other polymeric systems containing the unsubstituted azobenzene chromophore.