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.