Photo-alignment using adsorbed dichroic molecules

In this paper we report photo-alignment using low molecular weight dichroic materials. We produced photo-alignment by exposing thin films of dichroic materials such as methyl red, 4,4'-dihydroxyazobenzene and 4,4'-biphenol to linearly polarized light. The irradiation generates a preferred orientatio n of liquid crystals perpendicular to the polarization direction. The mecha nism of the photo-alignment process was studied. Alignment appears to be pr oduced by a single mono-layer of the dichroic material adsorbed on the subs trate. Polarized exposure produces anisotropic desorption and distribution of the remaining dichroic material. Photo-alignment of these materials requ ires the presence of polar groups in the molecules. Strong adsorption and s table alignment can be achieved by property matching the chemical character istics of the dichroic and surface materials. We hope to adjust the energy and tilt angle of the alignment layer by simply adsorbing mixtures of diffe rent dichroic materials.