Photoinduced Reorientation in Thin Films of a Nematic Liquid Crystalline Polymer Anchored to Interfaces and Enhancement Using Small Liquid Crystalline Molecules

Abstract

The photoinduced reorientation of the side-chain mesogens in nematic liquid crystalline (LC) polymer thin films triggered by the axis-selective photo-Fries rearrangements of side-chain phenyl benzoate moieties is studied to understand the regulation of the anisotropic nanostructures supported by LC polymers. The influence of the substrate surface in anchoring the side-chain mesogens near the interfaces is examined by comparing the reorientation of 30- and 120-nm-thick films. Irradiation with linearly polarized ultraviolet (UV) light and subsequent annealing causes the side-chain mesogen reorientation to align perpendicular to the electric field of the incident UV light. The inplane order in the 30-nm-thick films is lower than that in the 120-nm ones. On the other hand, the annealing period required for mesogen alignment is independent of the film thickness. It is suggested that the substrate surfaces anchor the LC mesogens to fix their orientation, rather than slowing down the reorientational motion. In addition, it is demonstrated that small LC molecules miscible with the nematic LC polymer enhance photoinduced reorientation through cooperative molecular interaction with the side-chain mesogens, remarkably accelerating the orientation and improving the inplane order of the unidirectionally aligned mesogens.

Polarized Fluorescence of N-Salicylideneaniline Derivatives Formed by In Situ Exchange from N-Benzylideneaniline Side Groups in Photoaligned Liquid Crystalline Copolymer Films

“…Many types of optical and display devices are fabricated by photoalignment of photosensitive polymeric films. − Two techniques have achieved photoalignment. One prepares a thin alignment layer for functional materials such as low-molecular-weight and polymerizable liquid crystals (LCs). − The other directly generates a molecularly oriented structure of a photosensitive film, and the photoinduced molecular reorientation produces a large optical anisotropy. ,,− In some cases, thermally stimulated photoinduced molecular reorientation occurs when a photoalignable material exhibits LC characteristics based on thermally induced self-organization. ,− Photoalignable LC polymers with cinnamate- or azobenzene-containing materials often display thermally stimulated photoinduced molecular reorientation. ,− These polymer films are applicable to birefringent optical devices and polarization-controlled diffraction gratings with a periodic molecular orientation structure. ,,− …”