ИСТИНА

The periodic helical supramolecular structure of cholesteric liquid crystals together with high sensitivity to the external fields make them very promising field-responsive materials for different applications in photonics, optical sensor creation, etc. Introduction of photochromic moieties in the polymer or low-molar-mass cholesteric systems allows one to create a large variety of novel materials with photoresponsive optical properties. This presentation describes our recent results in the field of photochromic cholesteric systems which could find application in different fields of photonics. The first part of the presentation is devoted to the creation of the stable polarization selective gratings by phototunable modulation of the helix pitch in polymer cholesteric mixture based on the nematic side-chain polymer doped with chiral-photochromic compound [1]. Such modulation was fabricated in the polymer mixture by a non-polarized UV-irradiation with spatially-modulated intensity that causes E-Z isomerization of a chiral-photochromic dopant. It was shown that the gratings recorded by UV-exposure through a mask are strongly selective to the handedness of circular polarized light. The obtained films open very interesting possibilities for development of materials for stable gratings in the entire visible spectra range. Both position and width of the spectral range of an efficient diffraction can be easily controlled by the UV-exposure and concentration of the dopant. In the second part of the presentation a novel type of rotatable diffraction gratings based on cholesteric liquid crystals with phototunable helix pitch will be described. The cholesteric liquid crystalline mixture with high helix pitch tunability and reversible photoinduced helix handedness inversion containing the azobenzene-based chiral-photochromic dopant was prepared. It was shown that this mixture under the hybrid (homeotropic – planar) boundary conditions spontaneously forms a well-oriented striped domain texture which acting as a phase grating. The obtained gratings rotate in both directions, clockwise and counterclockwise, under the action of UV and visible light, correspondingly. The total rotation caused by UV light illumination is ~1220o. The possibility of the creation of a variety of complex-organized structures by local light exposure of the cholesteric striped-domain texture was demonstrated (Fig. 1). The observed fascinating photooptical effects are of profound importance from scientific and applied points of view. Our results demonstrate promising properties of the elaborated systems for the development of novel photoresponsive materials for creation of specific functional elements for optics and photonics. This research was supported by the Russian Science Foundation (14-13-00379). Reference [1] A. Ryabchun, A. Bobrovsky, Y. Gritsai, O. Sakhno, V. Shibaev, J. Stumpe, ACS Appl. Mater. Interfaces, 2015, 7, 2554−2560. *) Author for Correspondence: bbrvsky@yahoo.com