Synthesis and Application of 1,8-Naphthalimide Derivatives Fluorescent Probe for Sequential Recognition of Cu²⁺ and H₂PO₄⁻

A naphthalimide Schiff base fluorescent probe (BSS) was designed and synthesized from 4-bromo-1,8-naphthalic anhydride, and its structure was characterized by ¹HNMR, ¹³CNMR, FTIR, and MS. Fluorescence emission spectra showed that probe BSS could realize the “turn-off” detection of Cu²⁺ in acetonitrile solution, detection process with strong specificity and excellent anti-interference of other metal ions. In the fluorescence titration experiments, fluorescence intensity of BSS showed a good linear relationship with the Cu²⁺ concentration (0–10 µmol/L), and the detection limit was up to 7.0 × 10^− 8 mol/L. Meanwhile, BSS and Cu²⁺ could form a 1:1 complex (BSS-Cu²⁺) during the reaction process. Under the same detection conditions, complex BSS-Cu²⁺ had specific fluorescence recovery properties for H₂PO₄⁻ and the whole process was not only fast (6 s) but also free of interference from other anions, with a detection limit was as low as 5.7 × 10^− 8 mol/L. In addition, complex BSS-Cu²⁺ could be successfully applied to the detection of H₂PO₄⁻ in actual water samples, which with excellent application prospects.