A highly selective colorimetric and fluorescent chemosensor for Cr2+ in aqueous solutions

[Display omitted] •A highly selective chemosensor for Cr2+ in aqueous solution has been developed.•The chemosensor allows colorimetric, spectrophotometric and fluorimetric detection.•The chemosensor was designed with rhodamine and coumarin moities.•The chemosensor was prepared through a copper catalyzed click cycloaddition. A new rhodamine-based chemosensor was synthetized through a modified copper-catalyzed [3+2]-cycloaddition of an azidocoumarin with an alkynyl-rhodamine. Its sensing properties toward various metal cations in aqueous solutions were investigated by colorimetric changes, UV–vis and fluorescence spectroscopies. The sensor exhibited a high selectivity for Cr2+ over Cr3+ and other divalent cations such as Cu2+, Mg2+, Zn2+, Ca2+, Cd2+, Co2+, Hg2+ and Ni2+. The linear range of detection by fluorescence spectroscopy is 0.07–3.5mM, with a detection limit of ca. 64μM. The binding mode of Cr2+ with the sensor was rationalized through experimental evidences.