Photo- and thermo-responsive switchable smart windows developed by the control of 3D molecular orientation of chiral liquid crystals with azobenzene molecular engineering

This study introduces a passive smart window whose state can be adjusted based on external stimuli, such as light and heat, by controlling the 3D molecular orientation of chiral liquid crystals (LCs). The 3D molecular orientation of chiral LCs is automatically controlled by azobenzene-based molecular engineering of the surface (AZ-COOH) and bulk molecular alignment (B1AZ) in the host LC (HLC). The resulting chiral LC (3D-ALC) smart windows are transparent under ambient conditions because of the vertically aligned HLC in the chiral smectic A (SmA*) monodomain. When exposed to UV light at room temperature, the 3D-ALC smart windows become opaque. This change occurs because the photoisomerization of the azobenzene-based alignment molecules transforms the SmA* monodomains into randomly dispersed multidomains. Above 35 °C (TNI of HLC), the HLC phase transforms into a focal conic state, resulting in an opaque state, regardless of UV light irradiation. The newly developed photo- and thermo-responsive smart window offers a new energy-saving window for maintaining comfortable indoor environments in automobiles and buildings.