Sunlight-driven smart windows with polymer/liquid crystal composites for autonomous control of optical properties

Abstract

We developed optically switchable smart windows driven by sunlight with polymer/liquid crystal (LC) composites containing azobenzene derivatives, which undergo trans–cis isomerization with high efficiency under sunlight. The composites exhibited high transparency in the initial state owing to homeotropic alignment of LCs, which was stabilized by polymer networks. Optical switching from the tranparent state to a light-scattering state was induced isothermally upon exposure to sunlight due to smectic A (SmA) to chiral nematic (N*) phase transition of LCs, triggered by trans–cis photoisomerization of the azobenzenes. The initial transparent state was restored in the absence of sunlight, resulting from N* to SmA phase transition induced by thermal cis–trans back isomerization of the azobenzenes. These autonomic smart windows utilizing only sunlight can be ubiquitously installed without additional artificial sources of energy.