“… 9 , 10 , 11 An interesting class of such optically VOC-responsive materials is given by liquid crystals (LCs), 12 , 13 which despite their liquid nature exhibit long-range orientational order along a direction called the “director.” 14 This gives them properties normally seen only in crystalline solids, such as birefringence and, in case of chiral LCs, structural color. 15 LCs have been shown to signal exposure to toluene, 16 , 17 , 18 , 19 , 20 acetone, 19 , 21 NO 2 , 22 CO 2 , 23 , 24 , O 2 , 24 amines, 25 cyclohexane and acetic acid, 26 chloroform and ethanol, 27 , 28 isopropanol, 29 tetrahydrofuran, methanol, tetrachloroethylene, 27 pyridine, hexane, and benzene 21 and to VOCs mimicking the nerve gas sarin. 30 , 31 , 32 , 33 Apart from making selectivity to specific VOCs easier than for typical consumer-grade electronic sensors, the non-electronic response of LCs, being fundamentally a VOC-induced change of optical characteristics driven by thermal energy alone, renders them ideal for autonomous sensors that require no power source.…”