1,2-Dithienyldicyanoethene Based Visible-Light-Driven Chiral Fluorescent Molecular Switch for Rewritable Multimodal Photonic Devices.

Abstract

Multifunctional light-driven chiral molecular switches or motors reversibly driven by visible light are currently in high demand towards the development of dynamic stimuli-responsive materials for fundamental studies and technological applications in advanced devices. Here we report the first example of 1,2-dithienyldicyanoethene based visible-light-driven chiral fluorescent molecular switch that exhibits reversible trans-cis photoisomerization in both isotropic and anisotropic solvents. The trans form of this distinct switch in solution is found to almost completely transform into the cis form accompanied by a 10-fold decrease in its fluorescence intensity within 60 s when exposed to green light (520 nm), while the reverse isomerization happens easily upon irradiation by blue light (405 nm). When doped into the commercially available achiral liquid crystal hosts, this molecular switch efficiently induces luminescent helical superstructure, i.e., cholesteric phase, due to its high helical twisting power (HTP). Owing to the large variation in its HTP value upon photoisomerization, the selective reflection wavelength of the induced cholesteric phases and the intensity of their circularly polarized fluorescence can be reversibly tuned using visible light of two different wavelengths. Optically rewritable photonic devices operating either in single fluorescent mode or reflective-fluorescent dual mode have been demonstrated using cholesteric films containing this visible-light-driven chiral fluorescent molecular switch. This new addition to the visible-light-driven chiral molecular switches toolkit could inspire the design and development of functional light-driven chiral switches for the fabrication of stimuli-responsive multifunctional soft materials and beyond.