A Sensitive Schiff Base Probe for UV-visible Spectral and Colorimetric Detection of Cu

In this study, we report an aminobenzamide-based Schiff base probe, designated as L [(E)-2-((2,3-dihydroxybenzylidene)amino)benzamide], developed for the selective and sensitive recognition of Cu2+, Al3+, and Fe3+ ions. The interaction of L with various metal ions was systematically investigated using UV-Visible spectroscopy. The UV-Vis analysis revealed the effective detection of Cu2+, Al3+, and Fe3+ ions, establishing L as a colorimetric probe in a DMSO: H2O (1:1, v/v) solvent system. Upon metal coordination, new absorption bands emerged at 418 nm (Cu2+), 388 nm (Al3+), and 680 nm (Fe3+). These bands originate from metal-induced modulation of the ligand’s native intramolecular charge-transfer (ICT) transition. Coordination through the phenolic oxygen, imine nitrogen, and amide nitrogen withdraws electron density from the donor segment, thereby altering and partially restricting the ICT process and generating distinct metal-specific charge-transfer transitions. The detection limits were determined to be 0.90 µM for Cu2+, 0.51 µM for Al3+, and 0.45 µM for Fe3+. Job’s plot analysis and electrospray ionization mass spectrometry (ESI-MS) confirmed a 1:1 stoichiometric complexation between L and each of the target metal ions. The proposed coordination modes were further supported by density functional theory (DFT) calculations. Moreover, the practical utility of L was validated through successful detection of trace Cu2+, Al3+ and Fe3+ ions in environmental water samples.