Highly Selective Turn-On Fluorescent Chemodosimeter for AlIII Detection through AlIII-Promoted Hydrolysis of C=N Double Bonds in the 8-Hydroxyquinoline Aldehyde Schiff Base

Fluorescent chemodosimeters based on small organic molecules are widely used in the detection of various analytes. However, chemodosimeters for metal ion detection are still limited to a few transition metals, such as Hg-II, Cu-II, Fe-III, Au-III, etc. In this work, a fluorescent chemodosimeter of 5-chloro-7-phenyliminomethyl-8-hydroxyquinoline (2) for the detection of Al-III is reported. Chemodosimeter 2 exhibits a turn-on fluorescence response to Al-III owing to an Al-III-promoted hydrolysis of carbon-nitrogen double bonds. This reaction yielded a 1-Al complex, which exhibited high fluorescence emission at 487nm based on inhibition of excited-state intramolecular proton transfer (ESIPT). Because of the specific catalytic ability of Al-III, the selectivity of 2 to Al-III is excellent both in aqueous solutions and in solid matrix. The fluorescence enhancement was as high as 582-fold and the turn-on fluorescence can be observed even by the naked eye upon an irradiation with a UV lamp. The detection limit of 2 for Al-III sensing is 54nmolL(-1) and the linear range is 0-50molL(-1). This work provides a new strategy for designing main-group-metal chemodosimeters based on small organic molecules.