Photo-Thermal Modulation of Cholesteric Liquid Crystals with a Dual Circularly Polarized Light Reflection Band

Abstract

In this study, we developed a cholesteric liquid crystal (Ch-LCs) composite with a dual (both right-and left-) circularly polarized light reflection band by utilizing a polymer template method, where a glassy Ch-LCs oligomer (GCLCO) with left-handed helical structure containing azobenzene dopant (AD) was infiltrated into the polymer template with right-handed helical structure. Photo-optical, thermal as well as glass-forming properties of the Ch-LCs film with a dual circularly polarized light reflection band were investigated, trans-cis (E-Z) photoisomerization of the AD in the GCLCO induced pitch length shortenings in response to the formation of the Z isomers by 365 nm ultraviolet (UV) irradiation, resulting that the reflection band of left-handed circularly polarized component of light in the Ch-LCs composite after UV irradiation exhibited a blue shift.What is more, the changed reflected color could be fixed in Ch glassy solid by rapid cooling from their Ch temperatures to below glass transition temperature (T g ), in which the photo and thermal isomerization of the AD could not influence the Ch pitch any longer and the color was stably stored. This technique has great applications such as tunable lasers, optical sensors, and security technology.