Synthesis of pi-Extended Coumarins and Evaluation of Their Precursors as Reactive Fluorescent Probes for Mercury Ions

Abstract

An efficient synthetic route to pi-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 Hg2+ ions. The vinyl ethers undergo hydrolysis promoted by Hg2+ 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 Hg2+ ions, as well as for the development of related reaction-based sensing systems.