Fluorogenic N,O-chelates built on a C2-symmetric aryleneethynylene platform: Spectroscopic and structural consequences of conformational preorganization and ligand denticity

Using π-extended aryleneethynylene as a rigid structural skeleton, a C2-symmetric bis(picolinate) ligand was prepared. Binding of zinc(II) or cadmium(II) ion to this formally tetradentate N2O2-chelate resulted in significant red-shifts and enhancement in emission. The metal–ligand interaction responsible for such structural change was investigated by isolation and characterization of a tetrazinc(II) complex, in which the picolinate group functions not only as terminal bidentate but also as bridging with its μ-1,3 carboxylate unit.

Graphical abstractC2-Symmetric tetradentate ligands built on the rigid bis(phenyleneethynylene) backbone support a tetranucler cluster of zinc(II) with enhancement in the longer-wavelength emission.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► New bis(picolinate) ligand built on a C2-symmetric π-conjugated backbone. ► Binding of zinc(II) or cadmium(II) to enhance longer-wavelength fluorescence. ► Picolinates as terminal and bridging ligands to support a tetrazinc(II) cluster.