Fluorescent Zinc(II) Complexes with a N,N,N-Tridentate Ligand Based on the Bis(imidazo[1,5-a]pyridine)methane Scaffold

A N,N,N-tridentate ligand (3,3 '-(2-(pyridin-2-yl)ethane-1,1-diyl)bis(1-methylimidazo[1,5-a]pyridine), L CH2Py) based on the bis(imidazo[1,5-a]pyridine)methane scaffold has been prepared through the introduction of a methylpyridine pendant arm. This functionalization provides an additional donor site, enabling a different coordination mode compared to previously reported bidentate systems. The reaction of this ligand with zinc(II) salts led to the formation of mononuclear complexes ([Zn(L CH2Py)X2], X = Cl, Br, I; [Zn(L CH2Py)Br](BF4); [Zn(L CH2Py)2](ClO4)2), which were fully characterized both in solution (NMR) and in solid state (X-ray). The tridentate coordination mode generates a rigid and stereochemically defined coordination sphere around the zinc center, resulting in the formation of chiral complexes, as supported by NMR analysis. The photophysical properties of ligand and complexes were investigated, revealing that all the derivatives exhibit intense blue fluorescence (lambda em = 453 nm for ligand, 419-437 nm for complexes), comparable to that observed for the parent system with unfunctionalized bis(imidazo[1,5-a]pyridine)methane (lambda em = 450 nm). These results demonstrate that the extension from N,N- to N,N,N-coordination enhances the structural rigidity and stereochemical complexity of the system while preserving the favorable emissive properties. This work further expands the scope of bis(imidazo[1,5-a]pyridine)-based ligands in coordination chemistry and highlights their potential as building blocks for the development of chiral luminescent materials.