High anchoring photoalignment material based on new photo-induced hole dipoles' mechanism

Abstract

Flat nonprofiled surface of photoalignment AtA-2 azo-dye layer possesses simultaneously low molecular orientation anisotropy and strong azimuthal anchoring energy. We explain how flat surface of alignment layer orients nematic liquid crystal and show the existence of the new photoalignment mechanism based on photo-induced hole dipole moments in the azo-dye layer. The dependence of anchoring energy coefficient on the square of dipole moments of the alignment layer and the liquid crystal layer is formulated, grounding the idea of chemical modification of AtA-2 azo-dye with molecular dipole moment ~16D to obtain novel high anchoring photoalignment material. The new AtA-0042 azo-dye with molecular dipole moment ~27.5D is synthesized and experimentally verified. Strong azimuthal anchoring energy over >1.4 × 10⁻⁴ J/m² is obtained for AtA-0042 photoalignment material layer with ~40 mJ/cm² exposure dose.