Reversible alignment change of liquid crystals induced by photochromic molecular films, 15. Convenient methods to prepare “command surfaces” by surface‐selective modification of thin films of poly(vinyl alcohol) with azobenzene units

A thin film of poly(vinyl alcohol) (PVA of different saponification degree) coated on a glass plate was subjected to a surface‐selective introduction of azobenzene moieties by treatment with a solution of 4‐(4‐hexylphenylazo) phenoxyacetyl chloride/pyridine or 4‐(4‐hexylphenylazo) phenoxybutanal /ptoluenesulfonic acid. Cells were fabricated by sandwiching a nematic liquid‐crystalline material between two surface‐modified glass plates. Alternating exposure to UV and visible light causes a reversible alignment of the liquid crystal molecules. Rubbing of the surface‐modified PVA resulted in an improved optical quality of the cell and enabled us to construct a photoresponsive twisted nematic cell. The advantages of the present method for preparing “command surfaces” are discussed from a practical point of view.