Photocontrol of LC alignment by disphenyl acetylene moieties at the LC-substrate interface

Abstract

The photocontrol of LC alignment was achieved using the surface-modificated LC cell with photoreactive molecules, called as command surface. In the photocontrol mechanism, a reorientation process with continuous isomerization of the photoactive molecule was proposed to be essential. To investigate effects of geometrical photoisomerization for LC alignment, we used diphenylacetylene (DPA) as a photoactive molecule with no photoisomerization. Our previous study shows that the re-orientation of chromophores at the LC-substrate interface play a crucial role in the photocontrol of LC alignment. In this study, 11-(4-(2-phenylethynyl)phenoxy) undecanoic acid (11DPA) was used as DPA moities and formed selfassembled complexes with poly-allylamine (PAA) on a substrate. The uni-directional LC alignment was observed on the LC cell using a substrate with DPA desity of 1nm²/molecule. However. no photoalignment was obsered in the case of a substrate with high DPA density (0.4nm²/molecule). Polarized absorption spectra of dichroic dye in the LC cell revealed that the direction of LC alignment was perpendicular to the LPL electricvector. In DPA substituted polymethacrylate films exhibited the parallel LC alignment to it. The reason for these differences of LC alignment direction was considered as a difference in photochemical reactions of DPA moieties.