Ultraviolet-Visible Light (UV–Vis)-Reversible but Fluorescence-Irreversible Chemosensor for Copper in Water and Its Application in Living Cells

An ultraviolet–visible light (UV–Vis)-reversible but fluorescence-irreversible chemosensor was developed for the detection of copper. Coordination between the probe, 2-pyridylaldehyde fluorescein hydrazone (FHP), and Cu2+ gave a reversible UV–Vis response, Storage of the probe–Cu complex resulted in hydrolytic cleavage of the NC bond, which released the fluorophore (ring-opened fluorescein hydrazine) and gave irreversible fluorescence. Thus, FHP becomes a multifunctional chemosensor, and its reversibility can be controlled by the reaction time. Cu2+ in living cells could be detected using FHP and general fluorescence methods.