A Calcium(II) Coordination Polymer Gel as a Highly Selective Fluorescent Chemosensor in Water for Cu(NO ₃ ) ₂

The development of metal‐organic gels as chemosensors for detecting metal ions has gained significant attention due to their critical roles in biological and environmental systems. Among these, the detection and quantification of Cu 2 ⁺ ions are particularly important, given the widespread industrial applications and the toxicity of its salts at elevated concentrations. Coumarin‐based fluorescent chemosensors have emerged as promising candidates due to their low toxicity and ease of functionalization. In this study, we report the synthesis and characterization of N ‐(7‐hydroxy‐4‐methyl‐8‐coumarinyl)‐leucine (H 2 muleu) and its metal complexes. Remarkably, the Ca 2 ⁺ complex forms a coordination polymeric (CP) gel, with gelation being highly specific to the choice of metal salt, ligand, and solvent. The resulting metal‐organogel exhibits intense blue fluorescence at 455 nm, with significantly enhanced emission compared to the free H 2 muleu ligand. Both H 2 muleu and its Ca 2 ⁺ complex demonstrate high selectivity and sensitivity as fluorescent chemosensors for Cu 2 ⁺ ions, especially as nitrate ions in aqueous media, with low detection limits. Notably, the fluorescence is completely quenched upon interaction with Cu 2 ⁺ ions, enabling naked‐eye detection under UV light. This work introduces a rare water‐soluble, highly selective, and sensitive chemosensor system for Cu 2 ⁺ ions, with potential applications in biological and environmental monitoring.