Fluorescent Janus ring siloxanes for detection of Au(III) and L-cysteine

Two new all -cis pyrene-substituted cyclic tetrasiloxanes (JR-01 and JR-02) are synthesized and studied as se-lective metal ion sensors. Both compounds exhibit solvent-and concentration-dependent excimer fluorescence emission at 482 nm. They also show highly selective fluorescence quenching by Au(III) ion with detection limits of 0.9 and 0.8 mu M for JR-01 and JR-02, respectively. Data from the Stern-Volmer's plots at various temperatures, zetasizers, NMR, and UV-Vis spectroscopy indicate a plausible mechanism involving the formation of a non -emissive Au(III) complex. An application of JR-01 as Au(III) sensor in real water samples reveals a good sensing efficiency which is comparable to the analysis result from ICP-QMS. In addition, when an excess amount of L-cysteine is added to the JR-01/Au(III) mixture, the fluorescence signal is restored and the 1H NMR data suggests that JR-01 remains intact. As an extension of this study, we successfully demonstrate the detection of L- cysteine by fluorescence turn-on process using the JR-01/Au(III) mixture with a detection limit of 14.0 mu M.