Command surfaces 15 [1]. Photoregulation of liquid crystal alignment by cinnamoyl residues on a silica surface

Abstract

The surface of a silica substrate plate was modified with a cinnamate moiety having a triethoxysilyl group at the ortho-position through a spacer. The plate was employed to assemble a cell filled with a nematic liquid crystal and exposed to linearly polarized 259 nm light to obtain homogeneous alignment. The direction of the alignment was perpendicular to an electric vector of the actinic light. On the contrary, the exposure of the cell to polarized light at 330 nm did not result in homogeneous alignment while the actinic light caused the disappearance of the chromophore. This wavelength effect on the azimuthal photoalignment suggests that the surface-assisted liquid crystal orientation is triggered by the reorientation of the E-isomer of the cinnamate group. This is in marked contrast to a proposed mechanism of a photoalignment by a thin film of a poly(vinyl cinnamate) derivative (Schadt et al., 1993, Jpn J. appl. Phys., 31, 2155); homogeneous alignment is induced by the axially selective photodimerization of cinnamate groups.