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

A group of lower rim modified lipophilic calix[4]arene derivative with phosphonic acid groups were used to fabricate the spin coated thin films. Chlorinated volatile organic solvents; chloroform, dichloromethane and carbon tetrachloride were selected for a deep investigation of their interaction with the thin films. The thin films possessed higher affinity to dichloromethane and chloroform vapor compared with the carbon tetrachloride vapor in the manner of the physical properties of the vapor molecules such as dipole moment, refractive index, vapor pressure and molar mass. The sensor parameters; response/recovery times, reproducibility, sensitivity, limit of detection and quantification were studied via the real time kinetic interaction. Sensitivity value up to 1.29×10-3 ppm-1 was calculated where the LOD and LOQ values were obtained down to 2-3 ppm and 7-13 ppm, respectively. Response times were in the range of 1-2 seconds and recovery times were between 2 to 4 s for all measurements. In other respects, the kinetic data was used to adopt to the Ficks’ law of diffusion model for the calculation of the diffusion constants and a two-region diffusion model was accepted where the values of the diffusion constants were found to be between 0.21-12.09×10-15 cm2 s-1 for the first region and 0.12–6.41×10-17 cm2 s-1 for the second region of the interaction. The nature of the complexation capacity was investigated via density functional theory calculations. The energy gaps between the LUMO and HOMO of calixarene complexes were calculated as 0.60 eV for carbon tetrachloride and 0.58 eV for dichloromethane complexes, whereas the energy gaps for calix-chloroform were found to be 0.51 eV, respectively. After overall assessment the highest sensing performance calix derivative was found to be CT4PA with four phosphonic acid groups. Theoretical data was found to be in good correlation with the experimental data.