Multi-responsible chameleon molecule with chiral naphthyl and azobenzene moieties

Abstract

A photochromic chiral molecule with azobenzene mesogens and a (R)-configuration naphthyl moiety (abbreviated as NCA₂M) was specifically designed and synthesized for the demonstration of chameleon-like color changes responding to multitudinous external stimuli, such as temperature, light and electric field. The basic phase transition behaviors of NCA₂M were first studied by the combination of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Based on the structure-sensitive X-ray diffraction results obtained at different temperatures, it was comprehended that the NCA₂M molecule exhibited the tilted version of highly ordered smectic crystal phase with 5.45 nm layer thickness. Chiral nematic (N*) liquid crystals (LC) with helical superstructures were formed by doping the NCA₂M photochromic chiral molecule in an achiral nematic (N) LC medium. By controlling the helical pitch length of N*-LC with respect to temperature, light and electric field, the wavelength of selectively reflected light from the N* photonic crystal was finely tuned. The light-induced color change of N*-LC film was the most efficient method for covering the whole visible region from blue to green and to red, which allowed us to fabricate remote-controllable photo-responsive devices.