Synthesis of π‐Extended Coumarins and Evaluation of Their Precursors as Reactive Fluorescent Probes for Mercury Ions

An efficient synthetic route to π‐extended coumarin derivatives and their precursors that contain amino substituents has been developed. The synthesis involves monosubstitution of 2,7‐dihydroxynaphthalene with dimethylamine through the Bucherer reaction. The extended coumarins emit at much longer wavelengths and with higher quantum yields relative to a related coumarin. Two vinyl ethers, precursors of the extended coumarins, were prepared and evaluated as reactive probes for Hg 2+ ions. The vinyl ethers undergo hydrolysis promoted by Hg 2+ ions to produce the extended coumarins at physiological pH (pH 7.4) and room temperature, which is accompanied by fluorescence in the “turn‐on” mode. The vinyl ethers do not respond to various other metal species. The extended coumarins and their precursors are versatile sensing platforms for Hg 2+ ions, as well as for the development of related reaction‐based sensing systems.