A Highly Selective and Sensitive Fluorescent Turn-on Probe for Al³⁺ Based on Naphthalimide Schiff Base

A simple and highly selective aluminium ion fluorescent probe (N-n-butyl-4-[3,3'-((2-aminoethyl)azanediyl)bis(N'-(2-hydroxy-3-methoxybenzylidene)-propanehydrazide)]-1,8-naphthalimide) (P-1) employing 1,8-naphthalimide as the fluorophore group and Schiff base as the recognition group has been successfully synthesized and systemically characterized. The structure of probe P-1 has been established by single crystal X-ray. The photophysical properties of probe P-1 revealed that the values of the fluorescence quantum yield are higher in non-polar solvents than in polar solvents. Compared with the free P-1, the fluorescence intensity of P-1 shows a significant fluorescence enhancement in the presence of Al³⁺ without any significant interference from other cations and anions. In addition, from the UV-vis titration, fluorescence titration,Job's plot and ¹H NMR spectra analysis, we could primarily confirm that three important coordinative sites of P-1 for Al³⁺ were from imine nitrogen and tertiary amine nitrogen and formed a 1:1 complex. The fluorescence intensity for the (P-1) showed a good linearity with the concentration of Al³⁺ in the range of 3.0-10.0 μM, with a detection limit of 8.65 × 10^-8 M and a binding constant (K_b) of 4.95 × 10⁴ M^-1. It is worthy of note that the probe P-1 was successfully applied in detection of Al³⁺ in Yellow River and tap water samples.