New variants of photosensitive polymeric mixtures: Reversible and irreversible photoregulation of helical supramolecular structure

New photosensitive cholesteric mixtures (I and II) containing tow different chiral-photochromic fragments were prepared. First mixture consists of phe nyl benzoate nematogenic homopolymer and two low-molar-mass (LMM) chiral-ph otochromic dopants based on cinnamic acid and azobenzene. Mixture II consis ts of cholesteric copolymers wit photosensitive azobenzene-containing side groups and LMM cinnamoyl-based dopant. Planar-oriented films of mixtures se lectively reflect light in visible and near infrared regions of the spectru m, UV and visible light irradiation leads to the changing of selective ligh t reflection wavelength which associated with E-Z photoisomerization and de creasing of the helical twisting power of chiral-photochromic fragments dur ing light action. It was shown that direction of the pitch of the helix cha nging can be easily controlled by incident light wavelength: in the case of mixture I UV irradiation leads to the long-wavelength shift of selective l ight reflection but visible light action leads to the short wavelength spec tral shift. In the cae of mixture II reverse behavior was observed. The spe cific features of the kinetics of forward and aback thermal processes were characterized. For such materials, their resistance wit respect to the repe ated "recording-erasing" cycles was tested, and the fatigue resistance was shown to be rather high. As was demonstrated, these mixtures containing chi ral groups sensitive to the light of different wavelengths maybe used for r eversible as well as irreversible recording of optical information.