Visible light, temperature, and electric field-driven rotation of diffraction gratings enabled by an axially chiral molecular switch

Abstract

The design and development of functional soft materials with responsive and adaptive properties that can be driven by multiple stimuli are necessary for fundamental scientific enquiry and technological applications in advanced devices. Herein, a novel visible light responsive axially chiral molecular switch with high helical twisting power (HTP) has been synthesized which shows good compatibility in a commercially available nematic liquid crystal (LC) host E7. The cholesteric liquid crystal (CLC) mixture fabricated using the chiral switch and LC E7 can be driven by visible light, temperature, and electric field. Reversible red, green, and blue (RGB) reflection colors upon visible light irradiation and temperature variation are achieved in the planar cell. When the CLC mixtures with different concentrations of the chiral switch are introduced into hybrid cells with planar and homeotropic boundary conditions, the spontaneous formation of diffraction gratings (DGs) occurs. Good quality DGs are obtained in the range of ∼1.85 ≤ d (cell thickness)/P ≤ ∼4.30. The stripes rotate clockwise continuously with the maximum rotation angle over 2π (383.1°) upon visible light (405 nm) irradiation, over π (192.4°) upon increasing temperature, and over π/2 (101.2°) upon applying electric field, respectively. Such multi-stimuli (visible light, temperature, and electric field) responsive in-plane rotation of the DGs shows great potential for beam steering, spectrum scanning, and beyond.