Azo Schiff bases as colorimetric and fluorescent sensors for recognition of F−, Cd2+ and Hg2+ ions

Abstract

The optical and colorimetric sensing properties of H₂L¹–H₂L³ for anions were investigated by the naked eye and UV-Vis and fluorescence spectroscopy. These chemosensors show visual changes towards anions like F⁻ and also towards cations such as Hg²⁺ and Cd²⁺ in DMSO. Yet, other anions such as Cl⁻, Br⁻, NO₃⁻, OAc⁻, HSO₄⁻, H₂PO₄⁻ and CN⁻ could not cause any color change. The ligands do not show any significant change on addition of other metal ions like Mn²⁺, Fe⁺², Co⁺², Ni²⁺, Cu⁺² and Zn²⁺. The binding constant (Ka) and stoichiometry of the host–guest complex formed were determined by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The anion sensing abilities of the receptors toward halide anions were also monitored by electrochemical techniques.