Cholesteric copolymers with spiropyrane side groups: Effect of the dye structure on photo- and thermotropic properties

Two new photochromic spiropyrane acrylic monomers differing by the length o f a flexible methylene spacer and the number of benzene rings were synthesi zed. Copolymerization of these monomers with a nematogenic and a chiral mon omers yielded two series of ternary cholesteric copolymers with a variable content of spiropyrane photosensitive side units. These copolymers exhibit a selective light reflection in the visible spectral region. Under the acti on of UV radiation, the copolymer films, with planar orientation form a mer ocyanine form of the dye whose absorption maximum coincides with the maximu m of selective light reflection. The kinetic laws of the photooptical behav ior of copolymers at various temperatures were studied. The effect of the s tructure of photosensitive side units on the kinetics of transition from th e spiropyrane form to the merocyanine one and vice versa was investigated.