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 Â 10 À4 J/m 2 is obtained for AtA-0042 photoalignment material layer with $40 mJ/cm 2 exposure dose.

Liquid-crystal q-plates with a phase core to generation vortex beams with controllable number of singularities

“…Thin film (20-30 nm thick) of the AtA-2 azo dye [37][38][39] formed the initial distribution of the director of a nematic LC in the element. Owing to the use of this azo dye, a new mechanism of LC photoinduced orientation was proposed on the basis of photoinduced hole dipoles [40], offering a high level of photosensitivity and a high energy of cohesion with LC molecules [41,42], high thermo-and photostability [37]. The power density of exposing polarized radiation was 15 mW/cm 2 .…”

44‐1: Invited Paper: Absorption Problem of Multilayer Optical Structures Based on High Anchoring Azo‐dye Photoalignment of Polymerizable Liquid Crystals

“…Thus the problem of high anchoring photoalignment has been explored, while its investigation has led to new generation of photoalignment materials based on reversible intermolecular bonds (RIB) [1]. Such materials apply new possibilities of the photoinduced hole-dipoles photoalignment mechanism [2] to provide azimuthal anchoring energy up to 10 -4 J/m 2 [3], while its films are not sensitive to air humidity [4] and can even be coated from water solvent [5].…”

Two-Dimensional Liquid-Crystal Photoalignment by Multiple Illumination Steps

“…Rotational diffusion is temperature-dependent, and in some models, rotational diffusion occurs in a potential that depends on the illumination . For some materials, additional mechanisms are suggested, for example, the electrical dipole of a remaining hole after trans–cis isomerization. , Experimental evidence for the reorientation of the long axis of photoalignment molecules under the influence of illumination is obtained by monitoring the linear dichroism through absorption spectroscopy in the visible range ,, or through IR spectroscopy . The director orientation and anchoring strength can also be (indirectly) evaluated after nematic LC is deposited.…”