Unpolymerized and Polymerized Discotic Liquid Crystal-Based Materials for Hydrogen Sulfide Gas-Sensing Applications

Hexa-peri-hexabenzocoronenene (HBC)-derived discotic liquid crystal (DLC)-based material carrying polymerizable diacetylene (DA) side chains, named HBC-1,2,4-Ph-DA-C12, was used to create a thin film as hydrogen sulfide (H2S) gas sensor. Both unpolymerized and polymerized DLC’s thin films show high performance for gas sensing. However, polymerized DLC-based thin film through ultraviolet (UV) irradiation demonstrated excellent mechanical properties and high environmental tolerance although slightly poorer gas sensing that the unpolymerized film. Resistivity measurement and UV–visible absorption spectra revealed that the DLC film functions as a gas sensor by exploiting the protic acid doping mechanism of H2S. At 60% and 80% relative humidity (RH) under N2 and air atmospheres, respectively, the sensors showed good repeatability, maintaining 50% accuracy under N2 after 30 days. These thin films exhibit a linear response to H2S concentrations of 1–10 ppm (maximal R2 = 0.9947) and a lower limit of detection of 1 ppm. Our results suggest that such DLC-based gas sensors are excellent at detecting H2S gas.