Calix[4]arene-triazine conjugate intermediate: optical properties and gas sensing responses against aromatic hydrocarbons in Langmuir–Blodgett films

Abstract

The detection of organic vapors by chemically based sensors was achieved with macromolecules having convenient molecular cavities. Addressed herein, a calix[4]arene derivative 25,27-(4-chloro-2-phenylamino-1,3,5-triazine)-26,28-dihydroxycalix[4]arene (C4AsTr) was synthesized and Langmuir–Blodgett (LB) thin films of this compound modified with heterocyclic units were examined for its optical properties and gas sensing capabilities against trace vapor of aromatic BTX hydrocarbons (benzene, toluene, xylene) through surface plasmon resonance technique. In line with this purpose, the experimental SPR data were fitted using the Winspall software to evaluate optical properties of the C4AsTr film. Such thickness and refractive index values of C4AsTr LB films were determined as 1.19 ± 0.02 nm for the thickness per monolayer, and 1.60 ± 0.04 for the refractive index. Exposed to above-mentioned organic vapors were measured with SPR technique, and the photodetector responses of these optical sensors, ΔI, were recorded as a function of time during kinetic process. In order to quantify real-time SPR data, early time Fick’s diffusion law was handled to extract the diffusion coefficients. There were two different regions observed with two slopes indicating that one belongs to fast surface diffusion and second one slow for bulk diffusion into C4AsTr LB film. All SPR results both theoretical and experimental indicated that C4AsTr optical LB thin-film sensors exhibit high response, a good sensitivity and selectivity for saturated benzene vapor than others. These optical thin-film sensors with aniline substituted triazine heterocycle have been potential candidates for organic vapor sensing applications with simple and low-cost preparation at room temperature.