Chlorinated vapor sensing performance of lipophilic calix[4]arene phosphonic acid based thin films: Sensor parameters, diffusion coefficients and theoretical calculations via density functional theory

Abstract

Agroup of lowerrim modified lipophilic calix[4]arene derivativewith phosphonic acid groupswere used to fabricate the spin coated thin films.Chlorinated volatile organic solvents; chloroform, dichloromethane and carbon tetrachloridewere selected for a deep investigation of theirinteraction with the thin films. The thin films possessed higher affinity to dichloromethane and chloroform vapor comparedwith the carbon tetrachloride vaporin the manner of the physical properties of the vapor moleculessuch as dipole moment,refractive index, vapor pressure and molar mass. The sensor parameters;response/recovery times,reproducibility,sensitivity, limit of detection and quantificationwere studied via the real time kinetic interaction. Sensitivity value up to 1.29 × 10−3 ppm−1was calculatedwhere the LOD and LOQ valueswere obtained down to 2–3 ppm and 7–13 ppm, respectively. Response timeswere in the range of 1–2 s and recovery timeswere between 2 to 4 sfor all measurements.In otherrespects, the kinetic datawas used to adopt to the Ficks’ lawof diffusion model forthe calculation of the diffusion constants and a two-region diffusion modelwas accepted where the values of the diffusion constantswere found to be between 0.21–12.09 × 10−15 cm2 s −1 for the firstregion and 0.12–6.41 × 10−17 cm2 s −1 forthe second region of the interaction. The nature of the complexation capacitywasinvestigated via density functional theory calculations. The energy gaps between the LUMO and HOMO of calixarene complexeswere calculated as 0.60 eVfor carbon tetrachloride and 0.58 eVfor dichloromethane complexes,whereasthe energy gapsfor calixchloroform were found to be 0.51 eV,respectively.After overall assessment the highestsensing performance calix derivativewasfound to beCT4PAwith four phosphonic acid groups. Theoretical datawasfound to be in good correlationwith the experimental data.