Heating effect on the liquid-crystalline octakis(hexylthio)zinc(ıı) phthalocyanine thin film sensor for the detection of chlorinated hydrocarbon vapors and ınteraction mechanism analysis using density functional theory

Abstract

A liquid-crystalline octakis(hexylthio)zinc(II) phthalocyanine (ZnPc2-B4) 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 ZnPc2-B4 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 ZnPc2-B4 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 degrees to 0.09 degrees when the ZnPc2-B4 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 ZnPc2-B4 thin film and the selected vapor. It was found that ZnCl, CCl, and NH interactions occurred. In addition, the interaction of Zn with the nucleophilic carbon atom of the vapor interacts with the pi-electrons of the C=C double bond. ZnPc2-B4 spun thin film sensor could be a potential candidate for optical sensor applications, such as environmental monitoring or VOC detection.