Highly Selective and Sensitive Fluorescent Probe for Copper (II) Ions Based on Coumarin Derivative with Aggregation-Induced Emission

Excessive accumulation of copper ions (Cu2+) in the environment and biological systems poses severe risks to ecological balance and human health, necessitating accurate detection and monitoring of Cu2+. Schiff base derivatives with favorable optical properties provide an efficient strategy for copper ion recognition. In this paper, fluorescent probe L (5-methyl-2-hydroxybenzaldehyde-(7-diethylaminocoumarin-3-formyl) hydrazone) was synthesized through a three-step reaction using 4-diethylaminosalicylaldehyde and diethyl malonate as starting materials. The structure of probe L was confirmed by melting point analysis, infrared spectroscopy, and nuclear magnetic resonance. Single-crystal X-ray analysis revealed that probe L crystallized into a triclinic lattice with space group P1−. Optical investigations, including UV–Vis spectroscopy, fluorescence spectroscopy, and aggregation-induced emission studies, demonstrated highly sensitive and selective fluorescence “turn-off” behavior of probe L towards Cu2+ ions in DMSO, with negligible interference from other metal ions. Job’s plot and crystallographic analysis revealed a 1:1 binding stoichiometry between probe L and Cu2+, forming the complex [Cu(L)]. Fluorescence titration experiments revealed a binding constant (Kb) of 5.2 × 106 L/mol and a detection limit of 7.8 × 10−7 mol/L, indicating excellent sensitivity. These results suggest that probe L has considerable promise for Cu2+ detection in aqueous environments, with potential applications in environmental monitoring and public health protection.