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.