Photoresponsive behavior of LCs doped with fluorescent materials

Abstract

AbstractLiquid crystalline (LC) molecules are known to reorient parallel to the light polarization when irradiated by linearly polarized light (a phenomenon known as light induced Frederiks transition). Dye‐doped LCs exhibit significantly enhanced photoinduced reorientation compared to undoped LCs. Although the reorientation behavior has been interpreted as a phenomenon based on interaction between the dye molecules and the electric field of light, the effect of the molecular structure on the photoinduced reorientation and details of the reorientational mechanism are not clear. In this study, photoresponsive behavior of LC systems doped with photostable fluorescent dyes were investigated. Sample cells were prepared by insertion of dye‐doped LCs into glass cells coated with n ‐octadecyl trimethoxy silane to obtain homeotropic alignment of LCs. Photoresponsive behavior of the LC system was evaluated by the self‐diffraction pattern formed upon irradiation of linearly polarized Ar+ laser beam at 488 nm. When the laser beam was incident on the sample cells, clear diffraction pattern was observed for the sample cell doped with Coumarin 6. Appearance of the diffraction ring indicates photoinduced reorientation of LCs. Thus, Coumarin 6 was found to act as a trigger for the photoinduced reorientation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)