Blue-Emissive Fluorescent Zinc(II) Complexes with Bis(imidazo[1,5-a]pyridine)methane Ligands

Three bis(imidazo[1,5-a]pyridine)methane derivatives (bis(1-methylimidazo[1,5-a]pyridin-3-yl)methane, LH; 3,3'-(ethane-1,1-diyl)bis(1-methylimidazo[1,5-a]pyridine) LMe; 3,3'-(2-phenylethane-1,1-diyl)bis(1-methylimidazo[1,5-a]pyridine), LBz) have been synthesized, and fully characterized in solution (1H and 13C NMR spectra) and in the solid state (X-ray). In particular, LH has been prepared in high yield (75 %) under very mild conditions (water, 60 degrees C), offering an alternative route to those reported in the literature. LMe and LBz have been obtained from LH by functionalization of the methylene bridge. The bis(imidazo[1,5-a]pyridine)methane compounds have been coordinated to a zinc(II) center, leading to tetrahedral complexes of general formula [Zn(LR)2](ClO4)2 (R=H, Me, Bz), which showed a bright fluorescent emission with (x,y) color coordinates very close to standard blue. TD-DFT have been employed to describe the Frontier Molecular Orbitals (FMOs) participating in electronic transitions, highlighting the main transition as 1(pi-pi*) transition in the bis(imidazo[1,5-a]pyridine)methane and a mixed intra-ligand (1ILT) and ligand-to-ligand (1LLT) transition in the complexes.