A novel colorimetric-fluorescent probe for Al3+ and the resultant complex for F- and its applications in cell imaging.

A novel quinoline-based Schiff-base probe QL had been synthesized, which could sequentially monitor Al3+ and F- in MeOH-H2O solution (v/v = 8/1, 0.01 M, HEPES buffer, pH = 7.3). The probe QL expressed a high selective and sensitive "OFF-ON-OFF" fluorescent response for Al3+ and F- (excitation at 460 nm and emission at 530 nm) accompanying visible color changed, which was ascribed to intramolecular charge transfer (ICT) process and chelation-enhanced fluorescence (CHEF) mechanism. The binding stoichiometry of QL with Al3+ was 2:1 counting on Job's plot and HRMS, while F- could pull Al3+ to depart from the complexation 2QL-Al3+ and released free QL. The limit of detections of probe QL for Al3+ and F- ions were calculated to be 0.10 μM and 0.50 μM. The 1H NMR experiments and density functional theory (DFT) calculations were carried out to further prove the binding mode between QL and Al3+. Furthermore, fluorescence imaging studies demonstrated that the probe QL was low cytotoxicity and could be applied to detect Al3+ and F- in living PC12cells.