Reversible Circularly Polarized Reflection in a Self-Organized Helical Superstructure Enabled by a Visible-Light-Driven Axially Chiral Molecular Switch.

Abstract

Development of light-driven functional materials capable of displaying reversible properties is currently a vibrant frontier from both scientific and technological points of view. Here a new visible-light-driven chiral molecular switch is synthesized and characterized. To the best of our knowledge, this is the first example of a chiral molecular switch in which the visible-light-driven azobenzene motif is directly linked to an axially chiral scaffold through a C-C bond. The chiral molecular switch exhibits trans-to- cis photoisomerization upon 530 nm irradiation and cis-to- trans isomerization upon 450 nm irradiation. The switch can thus be photoisomerized in both directions using visible light of different wavelengths, a promising attribute for device applications. It was found that this relatively rigid molecular switch exhibited a high helical twisting power (HTP) in liquid crystal hosts and a large change of HTP value upon photoisomerization. We achieved dynamic reflection tuning across the visible spectrum through incorporation into a self-organized helical superstructure, i.e., a cholesteric liquid crystal. We also demonstrated patterned photodisplays reflecting red, green, and blue circularly polarized light using these cholesteric films. Phototunable color displays were fabricated by selective light irradiation where the information can be reversibly hidden by applying an electric field and restored by applying either a mechanical force or an electric field of higher voltage.