A highly sensitive and selective fluorescent chemosensor for detection of Zn2+ based on a Schiff base

Abstract A Schiff-base fluorescent probe – 2-((E)-(quinolin-8-ylimino)methyl)quinolin-8-ol (H 7 L) was synthesized and evaluated as a chemoselective Zn 2+ sensor. Upon treatment with Zn 2+ , the complexation of H 7 L with Zn 2+ resulted in a red shift with a pronounced enhancement in the fluorescence emission intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Notably, this chemosensor could distinguish clearly Zn 2+ from Cd 2+ . Fluorescence studies on H 7 L and H 7 L–Zn 2+ complex reveal that the quantum yield strongly increases upon coordination. The stoichiometric ratio and association constant were evaluated using Benesi–Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job’s plot analyses. This chemosensor exhibits a very good fluorescence sensing ability to Zn 2+ over a wide range of pH.