Sensing Features and Detection Application of the Bishydroxycoumarin–Diaminopropane Conjugate and the Transmetalation Characteristics of Its Zn(II) Complex

A multifunctional coumarin-based fluorescent probe, HCDP, was synthesized via Schiff base condensation and characterized by FT-IR, UV–vis, NMR, and HRMS. It selectively detects Cu2+ in DMF–HEPES (9:1, pH = 7.4, v/v) through paramagnetic quenching, with a detection limit of 7.56 × 10–10 M. Spectroscopic and crystallographic studies confirmed the formation of a mononuclear Cu2+ complex (complex 1). The HCDP–Cu2+ ensemble exhibits reversible sensing of proline and was applied in logic gates, cotton swab sensors, and imaging in MDA-MB-231 cells, supported by live/dead and mitochondrial membrane potential assays. HCDP also forms a mononuclear Zn2+ complex (complex 2) that shows violet emission in DMF and cyan emission in aqueous media, enabling moisture sensing. In DMF, dual selectivity toward Zn2+ (blue shift) and Cu2+ (quenching) was observed, with detection limits of 10.21 nM and 4.70 nM, respectively. Competitive studies reveal a higher affinity for Cu2+, inducing single-crystal-to-single-crystal transformation of the Zn2+ complex upon exposure to Cu(OAc)2. The ensembles show reversible responses to histidine and proline, while complex 2 exhibits acid/base switching with TFA and TEA. Overall, HCDP demonstrates multifunctional sensing, enabling selective detection of metal ions and amino acids in aqueous and non-aqueous media for environmental monitoring and biological imaging applications.