Some Attempts to Regulate Alignment of Nematic Liquid Crystals by Various Photochromic Monolayers

Abstract

Surfaces of quartz plates were modified with photochromic compounds including azobenzene, stilbene, cinnamaldehyde, retinal, hemithioindigo, and spiropyran. Photochromic behavior was confirmed for these monolayered compounds except hemithioindigo which underwent irreversible photochemical reaction. The photo-induced alignment change between homeotropic and parallel modes of a nematic liquid crystal (LC) was obsersed only for LC cells which were made of quartz plates modified with azobenzene and stilbene. Attempts to regulate the alignment alteration photochemically with use of the spiropyran monolayer by simultaneous surface treatment with silylating reagents of long alkyl chains were failed. These imply that the change in molecular shape of the photochromic unit is closely related to the LC alignment change.