Effect of host liquid crystal structure on nonlinear molecular reorientation of oligothiophene-doped liquid crystals

Abstract

Nonlinear optical (NLO) materials whose optical properties change in accordance with incident light intensity are attracting much attention in various fields. Liquid crystals (LCs) exhibit the largest nonlinearity among functional materials due to their photoinduced molecular reorientation. In particular, doping dichroic oligothiophene dye into LCs increases the light sensitivity of materials based on the interaction between dyes and an optical-electric field. Furthermore, the absorbance of this LC system drastically increases through the dye molecules' reorientation, promising for application to the optical limiter; however, practical applications require better light sensitivity. In this study, we investigated the effect of the host LC structure such as fluorinated LCs on optical limiting behavior derived from nonlinear molecular reorientation. Irradiation of dye-doped LCs with a laser beam brought about molecular reorientation, and the transmittance decreased with an incident light intensity. Furthermore, the threshold light intensity for optical limiting behavior depended on the host LCs structure. Trifluorinated LCs effectively increased the light sensitivity of the dye-doped LCs compared to LCs without fluorine substituents. This result contributes to the material design for the lowthreshold optical devices utilizing the NLO of dye-doped LCs.