Impedance spectroscopic investigation of the effect of thin azo-calix[4]arene film type on the cation sensitivity of the gold electrodes

In this work, we report the impedance spectroscopic investigation of the effect of the thin film type on the selectivity of gold/azo-calix[4]arene electrodes. For this purpose, two C1 and C3 azo-calix[4]arene derivative molecules, used as thin films, are deposited by spin-coating process on the gold surface. These thin films were first studied using contact angle measurements. This revealed a less hydrophobic character for C3 thin film, which has been attributed to the presence of hydroxyl groups at the lower rim. The sensitivity study, by Electrochemical Impedance Spectroscopy (EIS), towards Cu2+ and Eu3+ cations, has showed that the C3 thin film is more sensitive and selective towards Eu3+ than C1. This best performance is due to the presence of two ester groups acting as clips and leading to more complexation stability. The EIS results were modeled by an appropriate equivalent circuit for the aim of elucidating electrical properties of thin films. This modeling has exposed that C3 thin film presents lower ionic conductivity and limited diffusion phenomenon at the interface. Highlights: → C1 and C3 azo-calix[4]arenes thin films are deposited on the gold surface. → The lower hydrophobicity for C3 was attributed to the presence of hydroxyl groups. → The C3 thin film is more sensitive and selective towards Eu3+ than C1 one. → This best performance is due to the presence of two ester groups acting as clips.