Characterization of a highly Al³⁺ -selective fluorescence probe based on naphthalimide-Schiff base and its...

A new fluorescent Al³⁺ -probe, N-allyl-4-[3,3'-((2-aminoethyl)azanediyl)-bis(N´-(2-hydroxybenzylidene)propanehy-drazide)]-1,8-naphthalimide (L), was designed and synthesized based on 1,8-naphthalimide. The probe L contains 1,8-naphthalimide moiety as the fluorophore and a Schiff base as the recognition group. The structure of L was determined by single crystal X-ray. L emission at 526 nm increased on addition of Al³⁺ under excitation wavelength at 350 nm. L exhibited high selectivity and sensitivity fluorescence emission towards to Al³⁺ in ethanol/Tris-HCl buffer solution (1:1, v/v, pH = 7.2) as compared with other tested metal ions. A good linearity with a correlation coefficient (R² ) of 0.99 was observed in the concentration range 2-10 μM. The binding constant and the detection limit of L for Al³⁺ were calculated to 2.6 × 10⁴  M^-1 and 0.34 μM, respectively. The results of experiments that including Job plot, ultraviolet-visible (UV-Vis) light titration, fluorescence titration, ESI-MS and ¹ H NMR titration, indicated a 1:1 stoichiometric complex between L and Al³⁺ . L was highly effective in monitoring Al³⁺ in real-life Yellow River and tap water samples.