A novel chemosensor for the distinguishable detections of Cu2+ and Hg2+ by off–on fluorescence and ratiometric UV–visible absorption

• A novel dual-functional chemosensor was developed to detect Cu 2+ and Hg 2+ . • Cu 2+ facilitated the opening of its rhodamine spirocycle. • Hg 2+ activated the opening of the rhodamine spirocycle and formed a new cycle. • Cu 2+ and Hg 2+ were detected by off–on fluorescence and ratiometric UV–Vis. • The chemosensor with low cytotoxicity could be successfully monitored Cu 2+ and Hg 2+ in living cells. A novel dual-functional chemosensor, derived from the conjugation of rhodamine B with a quinoline derivative (RHQ), was firstly synthesized with high efficiency and cost-effectiveness for the distinguishable detections of Cu 2+ and Hg 2+ via ring-opening and ring-forming mechanism. The chemosensor exhibits highly selective and distinguishable responses for Cu 2+ and Hg 2+ in CH 3 CN–H 2 O (4:1, v/v) with off–on fluorescence and ratiometric ultraviolet–visible (UV–Vis) absorption changes. Additionally, Cu 2+ is identified by opening a rhodamine spirocycle with a UV–Vis absorption band, at around 560 nm and fluorescence turn-on. Interestingly, Hg 2+ is discerned by opening the rhodamine spirocycle and by generating a new special cycle for the quinoline unit. Resultantly, there were two UV–Vis absorption bands at around 365 nm and 560 nm, which were accompanied by fluorescence turn-on. Moreover, the chemosensor can quantitatively detect Cu 2+ and Hg 2+ by off–on fluorescence and ratiometric UV–Vis absorption changes, respectively. Furthermore, the chemosensor with low cytotoxicity could be successfully administered to monitor Cu 2+ and Hg 2+ in living cells. This work may pay the way for the development of dual-functional chemosensor for quantificationally detecting metal ions in environmental and biological systems.