PHOTOCONTROL OF INPLANE ALIGNMENT OF A NEMATIC LIQUID-CRYSTAL BY A PHOTOCHROMIC SPIROPYRAN MOLECULAR LAYER

Quartz plates surface modified with a 6-nitrospirobenzopyran (SP) possessing a triethoxysilyl residue displayed photochromism. The polarity and interaction of SP with silanols at the surface are discussed on the basis of the absorption spectrum and thermal fading rate of the photomerocyanine form. When a nematic liquid crystal cell was fabricated with an SP-modified plate, azimuthal anisotropy of the nematic liquid crystal was caused by exposing the cell to linearly polarized UV light. The direction of the photo-induced homogeneous alignment was approximately perpendicular to the electric vector of the linearly polarized actinic light wave, and a photoimage was obtained by changing the polarization plane axis. The photo-induced in-plane alignment was scarcely altered even after prolonged storage at ambient temperature. Some attempts to regulate the alignment by irradiation with linearly polarized visible light for the reverse cyclization reaction failed.