Highly Selective Fluorescent Sensors for Hg²⁺ and Ag⁺ Based on Bis-triazole-Coupled Polyoxyethylenes in MeOH Solution

Graphical Abstract

Fluorescent chemosensors 6–9, bis-triazoles with a variable length polyoxyethylene chain, have been obtained by click chemistry. Of the 15 metal perchlorate salts screened, compounds 6–9 in MeOH showed selective fluorescence quenching towards only Ag⁺ and Hg²⁺. Under similar conditions, the control compound, a triazolylmethoxymethylpyrene, showed selective fluorescence quenching towards only Hg²⁺.

Abstract

Fluorescent chemosensors 6–9, with variable length polyoxyethylenes between two triazolylmethyl ether units, have been synthesized under “click” conditions in which the bis-triazoles and polyoxyethylenes were used as metal-ion binding sites and the pyrenes as fluorophores. Of the 15 metal ions screened, the fluorescence of chemosensors 6–9 in methanol solution was found to be selectively quenched by only Hg²⁺ and Ag⁺. In contrast, the fluorescence of control compound 10, a [(triazol-4-yl)methoxymethyl]pyrene, was quenched by only Hg²⁺. These results imply that the recognition of Hg²⁺ does not need the cooperation of two triazole groups. Binding constants for the interactions of 6–9 with Ag⁺ increased as the chain length of the polyoxyethylene increased. Finally, a very high selectivity of compound 9 towards Hg²⁺ in aqueous methanol solution was observed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)