Thermally, photochemically and electrically switchable reflection colors from self-organized chiral bent-core liquid crystals

Abstract

We report the synthesis and characterization of two new chiral 1,3-phenylene based five ring bent-core mesogens that combine the unique electro-optic characteristics of banana-shaped molecules with chiroptic properties. Azobenzene moiety incorporated as a linking unit in one of the rigid arms renders trans–cis isomerization property to the molecules while chirality is introduced by tethering chiral aliphatic terminal chains. Both compounds can self-organize into helical superstructure, i.e. cholesteric mesophase, which can selectively reflect light. The novelty of the helical self-organized superstructure reported here lies in its low molecular weight single component molecular system that is truly multifunctional so that the reflection band is tunable by three different external stimuli, i.e. temperature, light and electric field. A red shift in reflection colors is obtained by changing the temperature on cooling and by UV irradiation while a blue shift is seen by electrical field application. Due to the high applicability of azobenzene-doped liquid crystalline systems, we also evaluated the efficiency of these chiral bent-core molecules as chiral transfer agents and found that they behave similar to rod-shaped dopants whose chirality is a consequence of the presence of one chiral center.