From colorimetric sensing to molecular logic: A Schiff Base probe for dual Cu²⁺ and Fe³⁺ recognition

The development of efficient optical probes for the detection of biologically and environmentally important metal ions remains a significant research challenge. Herein, we report a Schiff base-derived colorimetric probe, (E)-2-((2-hydroxy-3-methoxybenzylidene)amino)benzamide (P), for the selective detection of Cu²⁺ and Fe³⁺ ions in a DMSO-H₂O (1:9, v/v) medium. Probe P exhibits distinct colorimetric responses toward the target ions, accompanied by the appearance of new absorption bands at 409 nm for Cu²⁺ and 690 nm for Fe³⁺, enabling naked-eye discrimination. The sensing response arises from coordination-induced electronic redistribution within the probe framework. The probe displays high sensitivity, with detection limits of 0.83 μM for Cu²⁺ and 0.62 μM for Fe³⁺. A 1:1 binding stoichiometry was supported by Job's plot and ESI-MS analyses, while FTIR studies provided additional evidence for the proposed binding mode. Furthermore, density functional theory (DFT) calculations provided insight into the electronic features of the resulting complexes. The practical utility of the probe was demonstrated through the determination of Cu²⁺ and Fe³⁺ ions in water samples with satisfactory recoveries. In addition, the probe was employed to construct molecular logic operations, including INHIBIT and YES gates. These results highlight probe P as a simple, sensitive, and effective platform for dual-ion sensing and molecular logic applications.