An imidazole-based fluorescent probe for the selective detection of copper (I) and copper (II) ions and potential...

A highly fluorescent benzil-bromosalicylaldehyde-based imidazole probe (L) has been synthesized with high yield, specifically designed for the selective recognition of copper ions (Cu⁺ and Cu²⁺). Probe L shows strong emission at 511 nm, which undergoes efficient fluorescence quenching upon binding with copper ions. Binding stoichiometry analysis revealed the formation of 1:1 and 2:1 complexes with Cu⁺ and Cu²⁺ ions, respectively, with corresponding quenching constants of 1.54 × 10⁵ M for Cu⁺ and 3.84 × 10⁴ M for Cu²⁺. The probe demonstrates high sensitivity with detection limits of 1.20 μM and 2.17 μM for Cu⁺ and Cu²⁺ ions, respectively, with negligible interference from other competing metal ions. Detailed spectroscopic investigations utilizing FT-IR, ¹H NMR, and HRMS, along with computational studies, elucidated the copper-binding mechanism that involves oxygen donor coordination and inhibition of the ESIPT process. These experimental spectroscopic investigations were instrumental in predicting frontier molecular orbitals and their energy gaps using computational calculations. Probe L enabled real-time monitoring of copper ions in environmental water samples, with L-impregnated cellulose test paper strips effectively detecting copper in solution and in solid-state applications. This is the first report to investigate spectrofluorimetric titration to identify distinct inflection points that differentiate between Cu⁺ and Cu²⁺ ions using probe L.