Алексей Бобровский » Публикация

Аннотация The state-of-the-art in the field ofmolecular design, synthesis, phase behaviour and photooptical properties of photochromic liquid crystalline (LC) side chain polymers, their blends with chiral and photochromic low-molar-mass dopants, hydrogen-bonded photochromic LC polymer systems, as well as photoresponsive LC dendrimers, is reviewed. The molecular architecture of the LC polymers and photochemical reactions of the main types of low-molar-mass achiral and chiral photochromes are briefly described. Recent advances in research dealingwith the synthesis and study of optical and photooptical properties of a series of photochromicLC polymers bearing nematogenic and photochromic side groups forming nematic, smectic and cholestericmesophases are considered. Among the various types of photochromic systems used to obtain the photoresponsive LC polymers the main attention focus on the so-called combined multifunctional systems composed of nematogenic, chiral and one or two photochromic fragments incorporated in thesamemonomerunits or entirely into themacromoleculeas individualmonomers.Thesystemsofbothtypesform chiral nematic (cholesteric) phase with helical supramolecular structure. Polymer cholesteric filmswith planar orientation exhibit a selective reflection of light in the visible or IR spectral range. The action of light leads to the isomerization of both chiral photochromic groups (or the photochromic group alone), which results in the variation of the helical twisting power of the chiral fragments. This process is accompanied by sharp changes in the supramolecular helical structure and the optical properties of the polymer. By properly selecting the copolymer composition and preparing blends of the LC polymers with low-molar-mass chiral and photochromic dopants, using hydrogen-bonded systems, it is possible to obtain materials with different characters of the lightinduced transformations. In particular, this provides the ability of controlling the pitch of the helix, the rate of helix twisting and untwisting, the width of the selective light reflection peak, etc. Thelast part ofreviewcoversarelativelynewclass ofLCcompounds—LCphotochromicdendrimers,whosephotochemicaland photooptical properties are briefly discussed. ThephotochromicLCcopolymers under consideration offernewpromising materials for reversible and irreversible black/white and colour data recording that can be used in optoelectronics, data storage (in optical memory systems), holography, and colour projection techniques and give rise to a new generation of video discs, flat light guides and coatings with controllable optical properties.