A Dual‐Functional “On‐Off‐On” Relay Fluorescent Probe for the Highly Sensitive Detection of Copper(II) and Phosphate Ions

A high‐efficiency dual‐functional on‐off‐on fluorescence probe: 2′–4′‐dihydroxydiphenyl‐8‐formyl‐7‐hydroxycoumarin hydrazine ( L ) based on photoelectron transfer mechanism (PET) was designed and synthesized, and its ion recognition characteristics were fully studied by spectroscopy. As expected, probe L shows highly sensitive to Cu 2+ in EtOH‐HEPES (20 mM v/v, 80 : 20, pH =7.40) solution, and its detection limit up to 6.14 ×10 −7  M. The stoichiometric ratio of L−Cu 2+ complex was determined as 1 : 1 based on 1 H NMR titration and ESI‐MS. Meanwhile, the resulted L−Cu 2+ complex shows good selectivity for the phosphoric acid family anion (H 2 PO 4 − , HPO 4 2− and PO 4 3− ), which denote probe L the dual‐function in rapid detection of Cu 2+ and phosphate family's ions.