Application of photosensitive polyimides as alignment layer to optical switching devices of a nematic liquid crystal

We have explored the change in alignment of a nematic liquid crystal, 4'-pe ntyl-4-cyanobiphenyl (5CB) with three types of photosensitive polyimide as the alignment layer by photoirradiation at 366 nm. The photosensitive polyi mide alignment layer induced a reversible change in alignment of 5CB. It wa s observed that the 5CB molecules became aligned from homogeneous alignment to homeotropic on photoirradiation with a d.c. electric field as a bias, a nd reversed to the homogeneous state when photoirradiation was ceased. This result indicates that optical switching could be repeated by on and off sw itching of the excitation light at 366 nm. The optical switching of the nem atic liquid crystal might be mainly due to a photophysical change in the po lyimide surface which is affected by the chemical structures of the polyimi des at the temperature at which 5CB exhibits a nematic phase. The optical s witching of nematic liquid crystals with photosensitive polyimides as the a lignment layer is a novel driving method for nematic liquid crystals.