Heating Effect on the Liquid-Crystalline Octakis(hexylthio)zinc(II) Phthalocyanine Thin Film Sensor for the Detection of Chlorinated Hydrocarbon Vapors and Interaction Mechanism Analysis Using Density Functional Theory

A liquid-crystalline octakis-(hexylthio)-zinc-(II) phthalocyanine (<b>ZnPc2-B4</b>) spun thin film sensor was fabricated to study the heating effect on the detection of chlorinated hydrocarbon vapors and to identify their interaction patterns at the reactive sites between the <b>ZnPc2-B4</b> thin film and vapor molecules. The surface plasmon resonance (SPR) technique was employed to collect sensor response data, which were analyzed to determine the optical and sensor parameters. After the heating procedure, the thickness of the <b>ZnPc2-B4</b> thin film decreased from 49.5 to 43.5 nm, and the sensor sensitivity for dichloromethane vapor decreased from 0.2864 to 0.1015% response/ppm. A similar heating effect on the SPR curve measurement occurred, and the SPR curve was shifted from 0.12 ° to 0.09 ° when the <b>ZnPc2-B4</b> thin film was exposed to the dichloromethane vapor. Atomic force microscopy results showed a compact and uniform surface with a surface roughness value of 2.77 nm. Density functional theory was used to elucidate interaction patterns between the <b>ZnPc2-B4</b> thin film and the selected vapor. It was found that Zn···Cl, C···Cl, and N···H interactions occurred. In addition, the interaction of Zn with the nucleophilic carbon atom of the vapor interacts with the π-electrons of the CC double bond. <b>ZnPc2-B4</b> spun thin film sensor could be a potential candidate for optical sensor applications, such as environmental monitoring or VOC detection.