New Variants of Photosensitive Polymeric Mixtures: Reversible and Irreversible Photoregulation of Helical Supramolecular Structure

Abstract

New photosensitive cholesteric mixtures (I and II) containing two different chiral-photochromic fragments were prepared. First mixture consists of phenyl benzoate nematogenic homopolymer and two low-molar-mass (LMM) chiral-photochromic dopants based on cinnamic acid and azobenzene. Mixture II consists of cholesteric copolymers with photosensitive azobenzene-containing side groups and LMM cinnamoyl-based dopant. Planar-oriented films of mixtures selectively reflect light in visible and near infrared regions of the spectrum. UV and visible light irradiation leads to the changing of selective light reflection wavelength which associated with E-Z photoisomerization and decreasing of the helical twisting power of chiral-photochromic fragments during light action. It was shown that direction of the pitch of the helix changing can be easily controlled by incident light wavelength: in the case of mixture I UV irradiation leads to the long-wavelength shift of selective light reflection but visible light action leads to the short wavelength spectral shift. In the case of mixture II reverse behavior was observed. The specific features of the kinetics of forward and back thermal processes were characterized. For such materials, their resistance with respect to the repeated “recording-erasing” cycles was tested, and the fatigue resistance was shown to be rather high. As was demonstrated, these mixtures containing chiral groups sensitive to the light of different wavelengths may be used for reversible as well as irreversible recording of optical information.