Molecular Reorientation of Nematic Liquid Crystals by Diarylethene-based Molecular Switch

Abstract

Previous studies showed that the trans-cis isomerization of azobenzene (azo) molecules can be used to manipulate molecular ordering of LCs. These properties have been widely exploited for responsive materials such as sensor, self-propelled colloids and soft actuators [2-5]. However, there are critical issues for the azo molecules that trans-to-cis transition occur only via UV light below 400 nm and return to the trans even in the absence of stimulus due to the metastable cis-isomer [3], which limits diverse applications. To overcome the inherent limitations, in this work, we propose diarylethene (DAE) as promising molecular switches for the design of responsive LC materials. As compared to azo molecules, DAE offers the access to (1) larger volumetric change between ring-opening and ring-closing isomers, (2) superior thermal stability of each state, (3) wide range of response wavelength (from visible to IR), and (4) high fatigue resistance after alternating cycles of light irradiation [1]. We demonstrate that the configuration of LCs can be controlled by the reversible photoisomerization of newly synthesized DAE-molecular switch. We found that DAE-open form induces planar anchoring of the LCs. Subsequently, when visible 1 is irradiated to a DAE-open form, DAE molecules change to a closed form which leads to vertical anchoring of the LCs (Figure 1). These findings allow one to enrich the set of control parameter. For instance, the use of various type of DAEs-molecular switches enable the design of wavelength-selective actuation in soft LC actuators, leading to the expansion of their application fields.