ESIPT-influenced C3-symmetry, disk-shaped fluorescence turn-on probe for Zn2+ based on melamine-naphthyl moiety with high affinity towards Cu2+ in CH3CN

Abstract

A C3-symmetry turn-on probe for Zn2+ based on the melamine-naphthyl moiety (H) was synthesized via a simple one-step Schiff base reaction mechanism. The photophysical properties were investigated using spectroscopic methods of UV–Vis and fluorescence. The chemosensing properties of H were investigated via colorimetric methods, using heavy metal cations as well as biological anions, in aqueous soluble acetonitrile (CH3CN). Subsequently, the probe demonstrated that it could discriminate few cations (Zn2+, Co2+, Ni2+ and Cu2+) and anions (CN−, F−, AcO− and OH−) via colorimetric methods, observable by naked eye. The colorimetric method was further complemented by spectroscopic methods of UV–Vis, where spectral shifts were observed upon adding molar quantities of these cations and anions, evidencing that, chemical interactions has taken place, between the host and guest. Interestingly, fluorescence analysis carried out, demonstrated that the ESIPT-steered probe was highly selective to Zn2+ only, among the cations and anions used, turning the initially non-fluorescent H into a dual emissive H-Zn complex upon excited at 380 nm. The selectivity of H towards Zn2+ was based on the geometrical complementarity through coordination induced charge transfer, upon binding. The DFT predictions were carried out to complement the experimental data.