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 °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(π-π*) 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.