A new fluorescent-colorimetric chemosensor based on a Schiff base for detecting Cr³⁺, Cu²⁺, Fe³⁺ and Al³⁺ ions

A new Schiff base derivative fluorescence-colorimetric chemosensor 2-hydroxy-5-[(2-hydroxy-1-naphthyl)methylideneamino]benzoic acid (H₃L), has been designed and synthesized. H₃L displayed high selectivity and sensitivity for detecting Cr³⁺, Cu²⁺, Fe³⁺ and Al³⁺ ions in DMF/H₂O (v/v = 1/1) solution. When Cr³⁺, Cu²⁺ or Fe³⁺ ions were added, the solution of H₃L in DMF/H₂O exhibited different color changes. While with the addition of Fe³⁺ or Al³⁺ ions, the solution of H₃L in DMF/H₂O displayed different fluorescence responses. The bonding modes and bonding ratios of H₃L and metal ions were explored by the Job's plot, ¹H NMR titration, and electrospray ionization mass spectrometry (ESI-MS). The detection limits of H₃L with Cr³⁺, Cu²⁺, Fe³⁺and Al³⁺ ions were 3.37 × 10^-7 M, 4.65 × 10^-7 M, 3.58 × 10^-7 M and 4.89 × 10^-7 M, respectively.