Redox-Triggered Orientational Responses of Liquid Crystals to Chlorine Gas

Surface-supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl-2 gas are reported. Computations identified Mn cations as candidate surface binding sites that undergo redox-triggered changes in the strength of binding to nitrogen-based LCs upon exposure to Cl-2 gas. Guided by these predictions, m-thick films of nitrile- or pyridine-containing LCs were prepared on surfaces decorated with Mn2+ binding sites as perchlorate salts. Following exposure to Cl-2, formation of Mn4+ (in the form of MnO2 microparticles) was confirmed and an accompanying change in the orientation and optical appearance of the supported LC films was measured. In unoptimized systems, the LC orientational transitions provided the sensitivity and response times needed for monitoring human exposure to Cl-2 gas. The response was also selective to Cl-2 over other oxidizing agents such as air or NO2 and other chemical targets such as organophosphonates.