A Turn-on Fluorescent Chemical Sensor Based on Imidazole-Schiff Base Structure for Al³⁺ Detection as Well as...

In this study, a novel imidazole-Schiff base fluorescent probe, EBI, was designed and synthesized. The molecular structure of EBI was systematically characterized by FT-IR, ¹H NMR, ¹³C NMR and HR-MS. This study found that this probe could exhibit highly sensitive and selective fluorescence responses to Al³⁺ in an EtOH/H₂O (1:1 v/v) mixed solvent. The optical properties of EBI were systematically investigated using fluorescence spectroscopy and UV-Vis absorption spectroscopy. The results showed that the binding of EBI with Al³⁺ could trigger a significant fluorescence enhancement effect, reaching a stable state within approximately 10 min, and that the interference from other common metal ions could be ignored. To further clarify its mechanism of action, various methods, including the Job plot, Benesi-Hildebrand experiment, ¹H NMR titration, and DFT calculation, were employed to thoroughly investigate the coordination behavior of EBI with Al³⁺. The study demonstrated that EBI and Al³⁺ formed a complex in a 1:1 molar ratio, with a detection limit (LOD) of 74.75 nM. The fluorescence quenching of EBI-Al³⁺ by PO₄^3- was also evident in the selected anion range. These results, based on the fluorescence "OFF-ON" mechanism, enable us to construct various types of molecular logic gates. This sensing system is capable of on-site, trace-level, real-time, and rapid detection of Al³⁺.