A Study of the photoorientation phenomena in cholesteric polymer systems containing photochromic diarylethene derivatives

Summary: Photoorientation processes in two cholesteric mixtures were studied. Mixture I contained a nematogenic phenylbenzoate homopolymer, a photochromic diarylethene dopant and a chiral dopant. Mixture II consisted of a binary comb‐shaped nematogenic copolymer with fluorescent perylene side groups and the same chiral and photochromic dopants. Irradiation of the mixtures with a polarized UV light did not induce photoorientation of the photoinduced “closed” form of the diarylethene dopant. However, the action of a polarized visible light on films of mixtures irradiated with UV light led to the appearance of dichroism. This phenomenon is associated with the photoselection process of the photochromic diarylethene molecules in the cholesteric matrix. An investigation of the kinetics of the photosensitized back photoreaction of the photochromic molecules in the cholesteric mixture showed that the polarized energy transfer from the fluorescent groups to the photochromic diarylethene dopant caused an increase in the photoselection rate. The thermal stability of dichroism in films of the mixtures was studied and it was shown that the disappearance of the dichroism of the diarylethene molecules occurred with a noticeable rate even at room temperature.

Scheme of photophysical and photochemical processes under the indirect excitation of diarylethene molecules.