The Dynamic Influence of Photoisomerization on Optical Reorientation in Absorbing Isotropic Liquid Crystals

The induced transient dichroism and the transient optical Kerr effect (OKE) response of azo-doped isotropic liquid crystals were studied in picosecond time scale. Photoisomerization occurs when the azo-dye molecules are resonantly excited. As a result, a significant enhancement of OKE signal was found in the dye doped liquid crystals with respect to the pure liquid crystals. The enhancement was attributed to the extra torque exerted on liquid crystals after anisotropic orientational distribution of trans and cis isomers were generated. A modified mean field theory model was applied to treat the interactions of trans and cis isomers with liquid crystals. A small-pump enhancement factor of 3.8 was obtained, which is comparable with that of the well-known anthraquinone dye doped LC system.