Design of Selective Chemical Reaction in Liquid Crystals via Organic Ionics

Abstract

Liquid crystals (LCs) are anisotropic fluids that have both long-range molecular ordering of crystal and fluidity of liquid. This combination of properties enables LCs to be the unique material that can sense a variety of stimuli, including nano- or molecular level events, and signal them into macroscopic optical output. The capability of LCs has provided a path to the design of promising reconfigurable materials in various field, such as display, optofluidics, and sensing. Particularly in the field of chemical sensing, however, their full potential has been hindered by their poor selectivity to a target chemical specie because only the chemical affinity between LCs and target chemicals has been considered. In this work, we propose simple and versatile design rules to control not only selectivity but also sensitivity by decorating the interface of LC films with organic ionics (OIs). We demonstrated the OI-LC sensors to selectively sense and optically report the exposure of a specific gas molecule (acetic acid) even at very low concentration (< 1 ppm). In addition, we experimentally and theoretically showed that their characteristics are precisely controllable by modulating the length of carbon chain and type of counter ion in OIs. This work was supported by the Korea National Research Foundation (NRF- 2021R1A4A1030944 & 2021R1A2C2095010).