Photoorientation of Liquid Crystalline Azo-Dendrimer by Nanosecond Pulsed Laser for Liquid Crystal Alignment

Abstract

Upon irradiation with nanosecond pulsed UV laser, surface periodic microstructure and photoorientation occurred simultaneously on the azobenzene functionalized liquid crystalline dendrimer films. The orientation of azo groups was perpendicular to the polarization of pulsed laser and dependent on the laser fluence. The in-plane orientation of azo groups presented parabola-shaped behavior with the increase of laser fluences. The out-of-plane reorientation of azo groups was closely related to thermal effect induced in the procedure of nanosecond pulsed irradiation, which led to the transformation of phase state of azo groups from smectic liquid crystal phase to isotropic phase. Annealing of irradiated film at its liquid crystalline temperature resulted in dramatic enhancement of in-plane orientation and out-of-plane redistribution of azo groups. Liquid crystal alignment on the irradiated film was controlled by a cooperative effect of surface topography and anisotropic molecular orientation simultaneously. Bo...