Dicyanomethylene-benzopyran-based alkynyl conjugatable near-infrared fluorescent probe for detection of fluoride anion

Near-infrared (NIR) fluorophore with one functional group, which can be utilized to conjugate other molecules, could meet various requirements just through structural modification, such as for regulating their subtle equilibrium between hydrophilicity and lipophilicity. Herein, considering the favorable photophysical properties of dicyanomethylene-benzopyran (DCMB) derivatives and the orthogonality of functional groups and the excellent biocompatibility of CuI-catalyzed click chemistry, the synthesis of azido and phenolic hydroxyl-bifunctionalized DCMB-based compound N3-DCMBOH is described, which can conjugate with other molecules by click chemistry. As a preliminary exploration, tert-butyldiphenylsilyl group and alkynyl-contained quaternary ammonium were successively conjugated onto N3-DCMBOH to construct NIR fluorescent sensor QA-DCMBSi for detection of F−. The dramatic absorption band change with 196 nm red shift and distinct NIR fluorescence enhancement at 718 nm, can be attributed to F− mediated cleavage of silicon-oxygen bond to release QA-DCMBOH, which was verified by MS spectrum.