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

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.