A quinoline-vinyl-dihydroxylphenyl linkage comprising a donor-π-bridge-acceptor structural motif, in which the quinoline serves as an electron-withdrawing core, has been synthesized and used as a fluorescent sensor (2) for the recognition of Al³⁺+ and F⁻ by colorimetry/fluorescence. The sensor 2 exhibited little fluorescence due to excited-state intramolecular proton transfer from the hydroxyl oxygens to the nitrogen of the quinoline moiety. By contrast, on coordination of Al³⁺+ or F⁻, sensor 2 afforded strong fluorescence. A reversible “off–on” optical switching mode has been constructed by sequential inputs from Al³⁺+ and F⁻ ions to the sensor 2 via different excitation and emission wavelengths. ¹H NMR and IR spectroscopic analysis revealed that the Al³⁺+ is coordinated to the quinoline nitrogen and phenolic oxygen atoms, whereas the F⁻ center is only coordinated by two phenolic oxygen atoms.
Redshaw, C., Li, J., Mu, L., Wei, G., Zeng, X., & Zhao, Y. (2014). A reversible and visible colorimetric/fluorescent chemosensor for Al³⁺+ and F⁻ ions with a Large Stoke's shift. Sensors and actuators. B, Chemical, 204(December), 450-458. https://doi.org/10.1016/j.snb.2014.07.048