COMMAND SURFACES .5. PHOTOREGULATION OF INPLANE REORIENTATION OF LIQUID-CRYSTALS BY AZOBENZENES LATERALLY ATTACHED TO SUBSTRATE SURFACES

An effective photochemical way to regulate the in-plane alignment of a nematic liquid crystal is presented. A quartz plate surface was modified with 4-hexyl-4'-hexyloxazobenzene substituted with a triethoxysilyl group through a spacer at the 2'-position to introduce the side-on type azobenzene unit on the surface. A liquid crystal hybrid cell was fabricated with the azo-modified plate and a quartz plate modified with lecithin. Irradiation of the cell with visible light linearly polarized for the n-pi* transition resulted in the in-plane reorientation of the liquid crystal molecules to afford a homogeneous alignment. The rate of the photoinduced reorientation was considerably enhanced by heating the cell above the nematic/isotropic transition temperature and was markedly stable toward heat and unpolarized light. The mechanism of the in-plane alignment is discussed, and the concept of a molecular rotor is proposed.