An Imidazo[1, 2-a]Pyridine Based Fluorescent Probe for the Continuous “on-off-on” Detection of Fe³⁺ and F⁻

An “on-off-on” fluorescent probe LK was synthesized from 2-benzoylpyridine and o-vanillin, which could sequentially detect Fe³⁺ and F⁻ in DMSO/H₂O solutions (v/v = 1/1, HEPES buffer, 1.0 mM, pH 7.0) with large Stokes shift (178 nm). LK exhibited not only high selectivity and sensitivity towards Fe³⁺ and F⁻, but also strong anti-interference ability to other ions. LK was coordinated with Fe³⁺ at a ratio of 2:1, with a binding constant (K_a) of 1.3 × 10⁴ M^− 1. The detection limits for Fe³⁺ and F⁻ were 6.9 × 10^− 8 M and 3.0 × 10^− 7 M, respectively. Due to its excellent sensing performance, LK was successfully applied in actual water samples and test papers for the detection of Fe³⁺ and F⁻.