A coumarin-thiourea conjugate as a fluorescent probe for Hg(II) in aqueous media with a broad pH range 2-12.

A coumarin-thiourea conjugate (1) behaves as a highly selective fluorescent probe for Hg(2+) in aqueous media. The probe 1 shows selective and quantitative fluorescence decrease upon Hg(2+) addition in aqueous media with a broad pH range, 2-12. Ab initio molecular orbital calculations reveal that the fluorescence decrease of 1 upon Hg(2+) addition is promoted by a Hg(2+)-induced desulfurization of the thiourea moiety, leading to a decrease in an intramolecular charge transfer (ICT) character of the excited-state coumarin moiety.