Schiff Base Compounds Derived from 5-Methyl Salicylaldehyde as Turn-On Fluorescent Probes for Al Detection: Experimental and DFT Calculations.

Using 5-methyl salicylaldehyde () as a reactant to react with different amines, 2-aminobenzimidazole (), 2-aminobenzothiazole (), and 2-aminopyridine (), respectively, three types of Schiff base fluorescent probes - were designed and synthesized for selective detection of Al in aqueous media. The structure of the compounds was acquired by H NMR, C NMR, and X-ray single-crystal diffraction. Furthermore, their photochromic and fluorescent behaviors have been investigated systematically by fluorescence spectra. Compounds - can exhibit high selectivity, sensitivity, and anti-interference properties towards Al in aqueous media. Among them, the limit of detection (LOD) of probe for Al is 2.81 × 10 M. Notably, the response times of probes - for Al are 90 s, 80 s, and 80 s, respectively, which are much faster than most previously reported probes. The coordination stoichiometry between compounds - and Al has been verified to be 1:1 through the Job's plot. After coordination with Al, the C=N isomerization of compounds - is inhibited, leading to the closure of the excited state intramolecular proton transfer (ESIPT) effect. At the same time, the fluorescence intensity is significantly increased through chelation-enhanced fluorescence mechanism (CHEF), which is confirmed by density functional theory (DFT) calculations. In addition, probes - can be potentially applied in the selective and high-precision detection of Al in environmental systems.