Chapter 5
Photo-Stimulated Phase Transformations in Liquid Crystals and Their Non-Display Applications
5.1 Introduction
The anisotropy of molecular shape is the prime factor responsible for the formation of liquid crystalline phases [1–3]. Manipulating this anisotropy by altering the chemical structure of the molecules has been the traditional way of stabilizing/destabilizing liquid crystal (LC) phases [4–7]. While this has been very efficient and has resulted in a wide variety of organic molecules exhibiting rich mesomorphic behavior, the possibility to control the anisotropy by a non-chemical external means has always been attractive. The modification in the shape of the molecules owing to conformational change driven by photoisomerization of certain systems responsive to light of a particular wavelength, called actinic light, has served this need very well. Photochemical pathways have the advantage over thermal and catalytic methods of giving mixtures rich in energetically unstable isomers. Photoisomerization is a photochemical process leading to an isomerization of a certain chemical entity, either by bond rotation, skeletal rearrangement, or atom/group-transfer [8] in chemical compounds. A number of organic compounds such as azobenzenes, stilbenes, alkenes are good examples of photoisomerizable molecular systems, which ...
