Photoinduced hole dipoles' mechanism of liquid crystal photoalignment

摘要

Polarized light absorption in photoalignment material induces anisotropic long-range interactions that orient liquid crystals. The main physical mechanisms behind anisotropic interactions are photocrosslinking and photodestruction of polymers, and photoisomerization and photorotation of azo dyes. Investigation of AtA-2 azo dye azimuthal anchoring versus exposure dose revealed the presence of an unusually strong anchoring peak at low doses, which is beyond our understanding of the known mechanisms. Here we explain these observations and demonstrate the existence of a photoalignment mechanism based on photoinduced hole dipole moments in the azo dye layer. Strong azimuthal anchoring energy >2 x 10(-4) J/m(2) is obtained with a <0.5 J/cm(2) exposure dose. (C) 2020 Optical Society of America