POLYMETHACRYLATES WITH BENZYLIDENEPHTHALIMIDINE SIDE-CHAINS, 2 - PHOTOCONTROL OF ALIGNMENT OF A NEMATIC LIQUID-CRYSTAL

The in-plane alignment photocontrol of a nematic liquid crystal (LC) w as performed by irradiation of thin films of polymethacrylates with be nzylidenephthalimidine (BPI) side chains with linearly polarized UV li ght. The orientational direction of LC molecules was perpendicular to the electric vector of polarized actinic light and in line with that o f BPI moieties in polymer films which were exposed to linearly polariz ed UV light. Prolonged polarized-light-irradiation leading to sufficie nt photodimerization did not result in the generation of a homogeneous alignment, indicating unequivocally that the photoalignment is caused specifically by polarized-light-induced E/Z photoisomerization. The l evel of the photoinduced LC alignment was improved by p-methoxyl subst itution at the benzylidene residue and by an appropriate choice of an irradiation wavelength giving Z-isomer as a predominant component at a photostationary state. Both effects are interpreted in terms of the m olecular shape of BPI favorable for the generation of LC photoalignmen t. Photodimerization under controlled polarized-light-irradiation cond itions enhanced considerably the thermal stability of LC photoalignmen t owing to the formation of crosslinks.