Hydrazone derivative bearing coumarin for the relay detection of Cu and HS in an almost neat aqueous solution and bioimaging in lysosomes.

A new morpholine functionalized coumarin-based fluorescent probe 1 was easily synthesized. The probe realized the sequentially detecting of Cu and HS in the HEPES buffer solution (20 mM, pH = 5.0). It made a turn-off fluorescence response to Cu by using a complex formation with a 2:1 binding mode, and the resulting complex was able to detect HS according to the displacement approach with a turn-on fluorescence response. The detecting limits of probe 1 for Cu and 1-Cu system for HS were calculated to be 26 nM and 88.5 nM, respectively. This "on-off-on" recognition process was demonstrated by ultraviolet-visible spectroscopy, fluorescence spectroscopy, using proton nuclear magnetic resonance studies, electrospray ionization mass spectroscopy, single crystal X-ray diffraction, and using density functional theory calculations. In addition, both cell imaging and co-staining experiments showed that the probe could be utilized to visually detect Cu and HS in lysosomes.