Photoregulation of liquid crystal alignment by a composite polymer film containing retinoic acid

The surface-assisted orientational photocontrol of nematic liquid crystal a lignment by composite polymer films containing all-trans retinoic acid is d escribed: The visual pigment derivative of retinoic acid teas immobilized i n poly(4-vinylpyridine) film through intermolecular hydrogen bonding betwee n carboxyl group oft he acid and pyridyl residues of the polymer. UV-vis sp ectral analysis indicated that photoirradiation of the polymer composite fi lm with 365 nm light lends to E/Z photoisomerization of the retinoic acid u nless exposure energies do not exceed about 1.0J/cm(2) while further irradi ation gives rise to irreversible consumption of the chromophore. Illuminati on of the films with linearly polarized light at 365 nm brought about photo dichroism, whose direction was perpendicular to the electric vector of the polarized light, as a result of the axially selective photochemical reactio ns of the all-trans-retinoic acid. A composite polymer film irradiated with linearly polarized 365 nm light exhibited the photocontrollability for azi muthal alignment of nematic liquid crystal molecules. The orientational dir ection of uniaxial liquid crystal alignment teas perpendicular to the polar ization plane of the actinic light, being consistent with the director of o ptical anisotropy induced by the polarization photo-chemistry of all-trans- retinoic acid. These results suggest that the surface-assisted photocontrol of liquid crystal alignment is attributable to the anisotropic orientation of the retinoic acid at an outermost surface of a photoactive composite po lymer film. Copyright (C) 2000 John Wiley & Sons, Ltd.