Structural parameters of Zn(II) complexes of 8-hydroxyquinoline-based tripodal ligands affect fluorescence quantum yield

Tripodal ligands containing 8-hydroxyquinoline moieties have been reported with strong binding but perplexing fluorescence properties. Herein we describe the synthesis, photophysical properties and structural characterization of three 8-hydroxyquinoline-based fluorescent Zn(II) probes. Incorporation of the chromophore into a tripodal scaffold resulted in femtomolar sensitivity to the analyte. All three ligands were determined to bind Zn(II) in a 1:1 metal–ligand stoichiometry. Strong zinc affinity was complemented by more than 10-fold fluorescence turn-on. An X-ray crystallographic study revealed very different ligand geometries in the zinc complexes that may influence their spectroscopic behavior.

Graphical abstractHerein we describe the synthesis, photophysical properties and structural characterization of three 8-hydroxyquinoline-based fluorescent Zn(II) probes. Structural parameters of the Zn(II) complexes affect fluorescence quantum yields.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Tripodal ligands with femtomolar zinc affinity. ► X-ray crystal structures of zinc complexes of the 8-hydroxyquinoline-based tripodal ligands. ► Photophysical properties of the 8-hydroxyquinoline-based tripodal ligands and their zinc complexes.