Facile synthesis of rhodamine-based highly sensitive and fast responsive colorimetric and off-on fluorescent reversible chemosensors for Hg2+: preparation of a fluorescent thin film sensor

Abstract

Fluorescence-active chemosensors (L1–L4), comprising a rhodamine scaffold and a pseudo azacrown cation-binding subunit, have been proposed and characterized as a fluorescent chemosensor for Hg²⁺. An on-off type fluorescent enhancement was observed by the formation of the ring-opened amide form of the rhodamine moiety, which was induced by the interactions between Hg²⁺ and the chemosensor. Upon the addition of Hg²⁺, an overall emission change of 350-fold was observed, and the selectivity was calculated to be 300 times higher than Cu²⁺ for receptors L2–L4. A polymeric thin film can be obtained by doping poly(methyl methacrylate) or PMMA with chemosensor L2. Such a thin film sensor can be used to detect Hg²⁺ with high sensitivity and can be recovered using diluted NaOH.