Light-responsive chiral photochromic liquid crystalline polymer systems

The authors reviewed their results obtained in recent years in the field of development of advanced optically controlled polymer systems based on photochromic cholesteric liquid crystalline (LC) polymers and their blends with each other and with low-molar-mass chiral and photochromic dopants. Recent advances in the research dealing with the design and study of photo-optical properties of photoresponsive LC polymers composed of nematogenic, chiral and one or two photochromic fragments incorporated in the same monomer units or entirely into the macromolecule as individual monomers are discussed. All polymer systems form cholesteric phase with a helical supramolecular structure. The light irradiation leads to the isomerization of one or two photochromic groups, which results in the variation in the helical twisting power of chiral fragments. This process is accompanied by dramatic changes in the supramolecular helical structure and optical properties of the LC polymer. This provides the possibility for controlling the pitch of helix, the rate of helix twisting and untwisting, spectral range, and the width of the selective light reflection. The photochromic LC systems offer new promising materials for reversible and irreversible colour data recording that can be used in optical memory systems (data storage), holography, colour projection techniques and give rise to a new generation of videodiscs, flat light guides and coatings with photocontrollable optical properties. (C) 2002 Elsevier Science B.V. All rights reserved.