Thermal- and photo-induced phase-transition behaviors of a tapered dendritic liquid crystal with photochromic azobenzene mesogens and a bicyclic chiral center

A ribbon-shaped chiral liquid crystalline (LC) dendrimer with photochromic azobenzene mesogens and an isosorbide chiral center (abbreviated as AZ ₃DLC) 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 AZ ₃DLC molecule exhibited the low-ordered chiral smectic (Sm*) LC phase with 6.31nm periodicity at a high-temperature phase region. AZ ₃DLC 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. Remote-controlled color: A ribbon-shaped chiral dendritic liquid crystal was newly synthesized, and its thermal and photo-induced phase behaviors were investigated with the combined techniques of the thermal, microscopic, and scattering methods (see figure).