A Rhodamine-Based “Off-On” Colorimetric and Fluorescent Chemosensor for Cu(II) in Aqueous and Non-aqueous Media
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A new rhodamine derivative (RhB-NSal) bearing an electron-withdrawing group –NO2 at the 5-position of 2-hydroxyphenyl moiety was synthesized and its sensing behaviors for Cu2+ in acetonitrile and aqueous acetate-buffer/acetonitrile (2/3, v/v, pH 4.8) media were investigated. In each medium, significant absorption and fluorescence enhancements accompanied by an instant color change from colorless to pink were observed for RhB-NSal upon addition of Cu2+. RhB-NSal binds with Cu2+ forming a 1:1 stoichiometric complex with an association constant of 6.72 (±0.03) × 104 M−1 and 4.23 (±0.03) × 104 M−1, respectively. RhB-NSal displayed high selectivity for Cu2+ over possibly competitive metal ions except that Fe3+ and Bi3+ ion can respectively bring about a little interference in absorption and fluorescence with its sensing for Cu2+. In dry acetonitrile, pronounced enhancements in the absorbance and emission of RhB-NSal were induced by Cu2+, with a detection limit of 0.49 μM, exhibiting higher sensitivity than that of a known analogue bearing no substituent on its phenol ring, RhB-Sal. In aqueous solution, RhB-NSal displayed likewise a high selectivity but a lower sensitivity for Cu2+ than that in acetonitrile, with a detection limit of 14.98 μM, still more sensitive than RhB-Sal in absorption. By virtue of these properties, RhB-NSal could be used as an “Off-On” fluorescent and colorimetric chemosensor for Cu2+ in acetonitrile medium, and be developed to be a promising candidate of “Off-On” eye-naked chemosensor for Cu2+ in a weakly acidic aqueous medium.
KeywordsChemosensor Copper (II) Electronic effect Rhodamine derivative Spectroscopic response
We thank the financial support from the Natural Science Foundation of Jiangsu Province (No. BK2012674) and from the research fund of Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province (No. AE201029).