Optical and organic vapor properties of Calix[4]arene based macrocyclic Langmuir-Blodgett thin films

Abstract

Surface Plasmon Resonance (SPR) optical chemical sensors based on 25,27-Bis(N-[[(2R)-2-hydroxy-3-[[(1R)-1-(hydroxymethyl)propyl]amino]propyl]asetamide))-26,28-dihydroxy-5,11,17,23-tetra(tert-butyl)calix[4]arene (NHDACx) films were fabricated to sense dichloromethane, acetone, and benzene at room temperature. Calix[4]arene based macrocyclic thin films, as gas sensing film, were fabricated by Langmuir-Blodgett (LB) thin film technique with different thicknesses, and characterized by SPR and UV-Visible spectrophotometer. The experimental SPR data were fitted using the Winspall software to evaluate optical properties of the NHDACx film such as the parameter of thickness and refractive index. Values of the thickness and refractive index of NHDACx LB films were determined as 1.29 +/- 0.06 nm for the thickness per monolayer, and 1.54 +/- 0.07 for the refractive index. Exposed to above mentioned organic vapors, the responses of the optical sensors, Delta I, were measured. Optical sensor with 7.9 nm NHDACx film shows higher response to the saturated concentration of all vapors than the others, due to the amount of the adsorbed vapor molecules onto the surface of NHDACx film. Sensing mechanisms are based on changing photodetector response and optical properties of the gas sensing element. As a result, NHDACx optical LB thin film sensors exhibits high response, a good sensitivity and selectivity for saturated dichloromethane vapor than other vapors. These optical thin film sensors were potential candidates for organic vapor sensing applications with simple and low cost preparation at room temperature.