A benzoxadiazole–thiourea conjugate as a fluorescent chemodosimeter for Hg(II) in aqueous media

A benzoxadiazole–thiourea conjugate (1) was synthesized and used for chemodosimetric detection of Hg2+ in aqueous media. The compound 1 shows a selective and quantitative fluorescence quenching upon addition of Hg2+. This is promoted via a Hg2+-induced desulfurization of the thiourea moiety, leading to a formation of an imidazoline derivative, 2. Ab initio molecular orbital calculation reveals that the formation of imidazoline moiety by the reaction of 1 with Hg2+ promotes a photoinduced electron transfer from the aniline moiety to the excited state benzoxadiazole moiety and results in fluorescence quenching.