Hg(II)‐Mediated Intramolecular Cyclization of Alkynyl Hydrazones: Towards a New Reaction‐Based Sensing Approach for Hg(II) Ions

Drawing upon an intramolecular cyclization/annulation reaction sequence mediated by Hg2+ ions, a BODIPY‐based fluorescent probe decorated with an alkynyl hydrazone motif responds rapidly and selectively to Hg2+ ions, with a detection limit of 29 nM and a fluorescence turn‐on ratio of 15‐fold. With the addition of Hg2+ ions, the BODIPY‐based alkynyl hydrazone transforms into a pyrazole ring to mediate a turn‐on emission response clearly observable to the naked eye under visible light excitation. We constructed a new family of a reaction‐based fluorescent probe, which shows remarkable fluorescence enhancement (15‐fold), a low detection limit (29 nM), and relatively quick response time (