Light-induced anchoring transition in a 4,4'-disubstituted azobenzene nematic liquid crystal

The behaviour of a liquid crystalline azobenzene material possessing a nematic phase was studied under UV illumination. It was found that a uniformly aligned planar sample of the azobenzene undergoes a reversible orientation transition to homeotropic; this can be interpreted as an anchoring transition caused by the photo-isomerization of the azobenzene moiety in the molecular structure of the nematogen. A simple model taking into account the changes in the molecular shape, as well as the magnitude of the molecular net dipole moment, and the changes in the surface density of the cis-isomers with UV exposure time is proposed to explain the light-induced anchoring transition in the azobenzene nematic.