A Benzophenanthrazine Schiff Base Fluorescent Probe for Selective Detection of Cu²

Copper ions (Cu²⁺) are essential trace elements but pose significant health and environmental risks at elevated concentrations. Development of fluorescent Cu²⁺ probes with high selectivity, rapid response, and wide applicable pH range is of great significance. In this work a benzophenanthrazine Schiff base fluorescent probe (D1) for selective and sensitive Cu²⁺ detection was presented. Probe D1 exhibited intense fluorescence emission at 517 nm that was quenched upon Cu²⁺ addition, achieving a detection limit of 0.53 µM with rapid response (less than 20 s). Job's plot and fluorescence titration fitting confirmed 1:1 binding stoichiometry between D1 and Cu²⁺, with an association constant of 5.0 × 10⁵ M^-1. Probe D1 showed good selectivity for Cu²⁺ over other metal ions in THF/H₂O (9:1, v/v) medium over a broad range of pH 4-11, and practical application in real water samples. FT-IR analysis, quantum yield measurements and density functional theory (DFT) calculations suggested Cu²⁺ coordination through the phenolic O and imine N atoms, supporting coordination-induced fluorescence quenching with a predominant static-quenching character.