Reversible alignment change of liquid crystals induced by photochromic molecular films

Abstract

The nematic director alignment in the liquid crystal cell was reversibly regulated by the geometrical isomerization of α-hydrazono- β-keto esters chemically linked on the substrate surface. Two methods for the surface modification were employed successfully. Method I was based on direct modification of substrates with α-hydrazono-β-keto ester units having a silylating group. Cells fabricated with these substrates showed altering reversible liquid crystal alignment through a combination of photoirradiation and heating. In method II, ω-acryloyloxyalkyl α-hydrazono-β-keto ester units were introduced through Michael addition to substrates modified with 3-aminopropyltriethoxysilane. The liquid crystal alignment in this case altered reversibly according to the reversible photoisomerization of the α-hydrazono-β-keto units on the substrates. The results strongly support the observation that a change in molecular shape, due to geometrical isomerization, is responsible for regulating the nematic director alignment.