Comparative Evaluation of Benzimidazole-Based Schiff Bases as Fluorescent Probes for the Sensitive and Selective Detection of Cu²⁺ Ions in Water Samples.

A new spectrofluorimetric method has been developed for the selective detection of Cu²⁺ ions based on a benzimidazole-containing Schiff base ligand. In this study, three structurally related Schiff bases (L1, L2, and L3) were synthesized and comparatively investigated for their fluorescence response in the presence of various cations. Among them, only L3 bearing ortho-hydroxyl groups on the aromatic rings exhibited a notable fluorescence quenching effect upon interaction with Cu²⁺, while L1 (para-hydroxyl substituted) and L2 (N, N-dimethylamino substituted) showed limited or no selectivity. The structure-function relationship revealed that the spatial orientation of donor groups plays a key role in metal coordination and signal transduction. The proposed method good sensitivity and selectivity toward Cu²⁺, with a linear response in the concentration range of 0-32 µg/L and a low detection limit of 0.98 µg/L, enabling quantification at relatively low concentrations. Furthermore, the method was tested with tap water samples. This work offers a potentially useful approach for Cu²⁺ determination but also highlights the importance of ligand geometry in fluorescent probe design.