ИСТИНА

Despite the long story on the investigations of cholesteric materials with phototunable helix pitch, there is a still growing interest in this research field. This is evidenced by a great body of recent papers devoted to the synthesis and study of new chiral-photochromic dopants. Such interest is associated with the recently opened opportunity to use these materials as photooptical switchers, phototunable lasers, photoactuation devices and micromotors, etc. This paper deals with the synthesis of new type of chiral photochromic dopants based on azobenzene derivatives possessing a very low rate of thermal back Z-E isomerization that makes them promising for different applications. Novel photosensitive azobenzene-containing substances with lactate- (1) and sorbitol-based (2) chiral fragments were synthesized to serve as chiral-photochromic dopants in cholesteric mixtures. Owing to the presence of chlorine or methyl lateral substituents in benzene ring the photoinduced Z-form of their molecules is highly stable. Several cholesteric mixtures using cyanbiphenyl and cyclohexane derivatives as nematic matrices were prepared. Photooptical properties of these cholesteric mixtures were studied and it was shown that UV-irradiation of the planar-oriented films results in a shift of the selective light reflection wavelength to a long-wavelength spectral region due to E-Z isomerization of azobenzene moieties (Fig. 1). This process is thermally and photooptically reversible and the rate of blue-light-induced helix twisting is comparable with the rate of the untwisting process, whereas the thermal relaxation completes only after ca. 40 days at room temperature (dopant 1). It was shown, that this value is almost two orders of the magnitude slower in comparison with non-substituted chiral-photochromic dopant also studied in this work. Obtained results demonstrate promising properties of synthesized compounds for creation of novel photoswitchable cholesteric materials. This research was supported by the Russian Foundation of Fundamental Research (13-03-00648, 13-03-12071 and 13-03-12456).