# 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

## TL;DR

This paper studies how heating affects a thin film sensor made of a liquid-crystalline zinc phthalocyanine compound for detecting chlorinated hydrocarbon vapors.

## Contribution

The study introduces a new analysis of the heating effect on sensor performance and interaction mechanisms using density functional theory.

## Key findings

- Heating reduced the sensor sensitivity for dichloromethane vapor from 0.2864 to 0.1015% response/ppm.
- Zn···Cl, C···Cl, and N···H interactions were identified between the thin film and vapor molecules.
- The thin film showed a compact and uniform surface with a roughness of 2.77 nm.

## 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 ° to 0.09 ° 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
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. ZnPc2-B4 spun thin film
sensor could be a potential candidate for optical sensor applications,
such as environmental monitoring or VOC detection.