Irreversible phase and anchoring transitions of chiral azodye-doped nematic liquid crystal triggered by photostimulation

Reported herein are the simultaneous phase and anchoring transitions of the chiral azodye-doped liquid crystal (LC) mixture. The transitions are influenced by photostimulation and are stable against light and thermal treatments. The photochromic trans state of the azobenzene molecule used in the study is mesogenic with a chiral nature. The photoinstigated cis form of the molecule has a much-enhanced dipole moment with a broken chromophore symmetry. Due to the high dipole–dipole interaction, the cis-state molecules stack together and form nano-sized aggregates. Subsequently, the cis aggregates get phase-separated, resulting in the chiral- to achiral-phase transition of the host LC. The phase-separated cis aggregates diffuse to the interface between indium-tin-oxide and LC and modify the surface, causing planar to homeotropic anchoring transition of the host LC. The stability and irreversibility of the transition, and the fact that there is no need for pre-treatments for LC alignment, provide a fascinating opportunity for LC device applications.