Thermal‐ and Photo‐Induced Phase‐Transition Behaviors of a Tapered Dendritic Liquid Crystal with Photochromic Azobenzene Mesogens and a Bicyclic Chiral Center

Abstract

A ribbon-shaped chiral liquid crystalline (LC) dendrimer with photochromic azobenzene mesogens and an isosorbide chiral center (abbreviated as AZ3 DLC) was successfully synthesized and its major phase transitions were studied by using differential scanning calorimetry (DSC) and linear polarized optical microscopy (POM). Its ordered structures at different temperatures were further identified through structure-sensitive diffraction techniques. Based on the experimental results, it was found that the AZ3 DLC molecule exhibited the low-ordered chiral smectic (Sm*) LC phase with 6.31 nm periodicity at a high-temperature phase region. AZ3 DLC showed the reversible photoisomerization in both organic solvents and nematic (N) LC media. As a chiral-inducing agent, it exhibited a good solubility, a high helical-twisting power, and a large change in the helical-twisting power due to its photochemical isomerization in the commercially available N LC hosts. Therefore, we were able to reversibly "remote-control" the colors in the whole visible region by finely tuning the helical pitch of the spontaneously formed helical superstructures.