Redox‐Triggered Orientational Responses of Liquid Crystals to Chlorine Gas

• Published in: Angewandte Chemie International Edition 2018-07, Vol.57 (31), p.9665-9669
• Main Authors: Szilvási, Tibor, Bao, Nanqi, Nayani, Karthik, Yu, Huaizhe, Rai, Prabin, Twieg, Robert J., Mavrikakis, Manos, Abbott, Nicholas L.
• Format: Article
• Language: English
• Subjects: anchoring transitions; Binding sites; Cations; chemistry; Chlorine; Cl2 detection; Crystals; Exposure; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Liquid crystals; Manganese dioxide; Microparticles; Nitrogen dioxide; Organic chemistry; Organophosphonates; Oxidation; Oxidizing agents; Perchlorate; Perchloric acid; Pyridines; redox chemistry; Salts; sensors; Thick films
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201803194

Surface‐supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl2 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 Cl2 gas. Guided by these predictions, μm‐thick films of nitrile‐ or pyridine‐containing LCs were prepared on surfaces decorated with Mn2+ binding sites as perchlorate salts. Following exposure to Cl2, 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 Cl2 gas. The response was also selective to Cl2 over other oxidizing agents such as air or NO2 and other chemical targets such as organophosphonates. Passive sensors for Cl2 using LCs: Guided by computational chemistry, Cl2‐triggered changes in the oxidation state of Mn2+ cations on surfaces were shown to change the binding strength of liquid crystals (LCs) to surfaces and thus trigger optical responses in the LCs. The sensitivity, selectivity, and dynamic response of the LCs to Cl2 makes them suitable for use in wearable sensors for monitoring personal exposure to Cl2 gas.