Effect of Host Structure on Optical Freedericksz Transition in Dye-Doped Liquid Crystals

Abstract

The optical Freedericksz transition (OFT) can reversibly control the molecular orientation of liquid crystals (LCs) only by light irradiation, leading to the development of all-optical devices, such as smart windows. In particular, oligothiophene-doped LCs show the highly sensitive OFT due to the interaction between dyes and an optical-electric field. However, the sensitivity is still low for the application to optical devices. It is necessary to understand the factors in LCs affecting the OFT behavior to reduce the sensitivity. In this study, we investigated the effect of the host LC structure on the OFT in oligothiophene-doped LCs. The threshold light intensity for the OFT in trifluorinated LCs was 42% lower than that in LCs without fluorine substituents. This result contributes to the material design for the low-threshold optical devices utilizing the OFT of dye-doped LCs.

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

“…For input and output power, the reflectance at the air-glass interface was considered based on the Fresnel equation, and the corresponding transmittance was calculated. [44] The prepared LC samples exhibited an optically transparent yellow color due to the absorption of TR5 (Figure 3a). Conoscopic micrographs of the samples showed a clear isogyre (Figure 3b).…”

“…We believe that the results provide crucial knowledge for designing a highly sensitive NLO system using dye-doped LCs. [44] The molecule structures of host LCs and a guest dye are shown in Figure 1. The mixing ratio of the compounds and the procedure of cell fabrication with homeotropic alignment layers were the same as in the previous report [44] .…”

“…[44] The molecule structures of host LCs and a guest dye are shown in Figure 1. The mixing ratio of the compounds and the procedure of cell fabrication with homeotropic alignment layers were the same as in the previous report [44] . The dyedoped host LCs were injected into glass cells by capillary action.…”

“…We defined the five prepared LC cells depending on the compounds as follows: TR5/5CB; TR5/(5CB F-LC1); TR5/(5CB F-LC2); TR5/(5CB F-LC3); and TR5/(5CB F-LC4). [44] . Copyright 2022 by the authors.…”

“…Licensee MDPI, Basel, Switzerland. [44] The initial molecular orientation in the samples was evaluated by polarized optical microscopy (POM) and polarized UV-vis absorption spectroscopy. The conoscopic micrographs were obtained using a polarized optical microscope (BX53-P, Olympus Corp., Tokyo, Japan) equipped with an interference filter at 546 nm.…”