Solvent-dependent selective fluorescence sensing of Al3 + and Zn2 + using a single Schiff base

The selective assay of Al3 + and Zn2 + ions is reported using fluorescence enhancement of a simple Schiff base receptor 1 (1 = 1-((E)-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)naphthalen-2-ol) in aqueous solvents. The Schiff base receptor 1 showed a turn-on fluorescence in the presence of Al3 + in a mixture of methanol–water, as a result of a restricted Cdouble bond; length as m-dashN isomerization mechanism. The ion selectivity of 1 could be switched for Zn2 + by swapping the solvent from methanol–water to DMF–water mixture. In particular, this chemosensor could clearly distinguish Zn2 + from Cd2 +. The binding properties of 1 with the metal ions were investigated by UV–vis, fluorescence, electrospray ionization mass spectroscopy and 1H NMR titration.