An easy-to-synthesize multi-photoresponse smart sensor for rapidly detecting Zn2+ and quantifying Fe3+ based on the enol/keto binding mode

Abstract

A readily available 4-diethylaminosalicylaldazine-modified fluorene Schiff base (EASA-F) was designed and synthesized through a one-step reaction. EASA-F exhibited a fast fluorescence OFF–ON response to Zn²⁺ and an OFF–ON–OFF behavior to Fe³⁺ in aqueous acetonitrile. This was synchronously accompanied by diverse absorption-ratiometric changes and colorimetric changes that were observable by the naked eye; these changes were attributed to the inhibition of CN isomerization and ESIPT processes in addition to the ICT mechanism that resulted from the different binding modes between the enol–keto species and Zn²⁺/Fe³⁺. Moreover, the multi-optical responses of EASA-F to Zn²⁺/Fe³⁺ were reversible with EDTA as the chelating ligand. These findings combined with the dual-optical changes from the metal displacement of EASA-F–Zn²⁺ by Fe³⁺ make the single-molecule EASA-F a real-time versatile sensor for sensitively detecting Zn²⁺ and accurately quantifying Fe³⁺.