Synthesis of Coumarinylhydrazone Fluorescent Probe and its Relay Recognition of Cu²⁺ and HPO₄²

A novel coumarinylhydrazone fluorescent probe L was designed and synthesized from 4-(diethylamino)salicylaldehyde, its structure was characterized by NMR, IR. Fluorescence emission spectra showed that in ethanol solution, probe L could form a 1:1 complex L-Cu²⁺ with Cu²⁺ to realize the "turn-off" detection of Cu²⁺ with high specificity and sensitivity (3.7 × 10^-7 mol/L). Meanwhile, the complex L-Cu²⁺ had a specific fluorescence-enhanced response to HPO₄^2- with a detection limits down to 5.6 × 10^-7 mol/L and was resistant to the effects of many common anions (NO₂^-, N₃^-, CO₃^2-, SO₃^2-, HPO₄^2-, I^-, Br^-, F^-, HCO₃^-, SO₄^2-, NO₃^-, Cl^-, CH₃COO^-, Cr₂O₇^2-, S₂O₃^2-, P₂O₇^4-). Detection mechanism could be HPO₄^2- captured Cu²⁺ of the complex and released the free ligand L. At last, the complex L-Cu²⁺ was successfully applied to the determination of HPO₄^2- in different environmental water samples, and the spiked recoveries ranged from 98.05% to 108.18% and the relative standard deviations of 0.75% ~ 2.9%, which had good application prospects.