Photo-optical liquid crystal cells driven by molecular rotors

Photochemical regulation of in-plane alignment of a nematic liquid crystal is presented. A quartz plate surface was modified with 4-hexyl-4′-hexyloxyazobenzene substituted with triethoxysilyl group through a spacer at the 2′ position to introduce the side-on type azobenzene unit of the surface. A liquid crystal hybrid cell fabricated with the azo-modified plate was irradiated with linearly polarized visible light for the n-π* transition. This resulted in the in-plane reorientation of the liquid crystal molecules to afford homogeneous alignment. Discussion is made on the mechanism of the in-plane alignment regulation, and the concept of a molecular rotor is proposed.