Selective Chemical Report based on Liquid Crystals integrated with Organic Ionics

Abstract

Liquid crystals (LCs), which have amplification property by anisotropic nature and long-range molecular ordering, lead molecular scale interaction to be magnified to visible scale [1]. Therefore, LCs have been used for reporting a variety of chemical stimuli. However, the relatively low selectivity to specific chemicals was pointed out as a problem. Here we propose versatile design rules to control not only selectivity but sensitivity by decorating the interface with organic ionics (OIs). We demonstrated the OI-LC film immediately reacts and optically reports the exposure of a specific gas molecule (acetic acid) at very low concentration (< 1 ppm). We confirmed LC molecule electrostatically and physically interacts with OI causing vertical orientation of the LC film. In the exposure of acetic acid, however, carboxylic group interrupts the existing interaction, changing LC orientation. Furthermore, we showed their characteristics are controllable by modulating the length of carbon chain and type of counter ion in OIs. Computational simulation represents good agreement with our experimentally proposed mechanism. This work was supported by the NRF (2021R1A4A1030944 & 2021R1A2C2095010)