화학공학소재연구정보센터
Inorganic Chemistry, Vol.57, No.7, 3587-3595, 2018
Coordination-Driven Self-Assembly of Ruthenium Polypyridyl Nodes Resulting in Emergent Photophysical and Electrochemical Properties
Ruthenium polypyridyl complexes are among the most studied molecular species for photochemical applications such as light-harvesting and photocatalysis, with [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) serving as an iconic example. We report the use of the [Ru(bpy)(2)](2+) fragment as a 90 degrees acceptor tecton (M) in coordination-driven self assembly to synthesize a M4L4 metallacycle (L = 4,4'-bipyridine) and a M6L4 truncated tetrahedral cage [L = 2,4,6-tris(4-pyridyl)-1,3,5-triazine]. The M6L4 cage possesses emergent properties attributed to its unique electronic structure, which results in increased visible-light absorption and an emission band that decays biexponentially with times of 3 and 790 ns. The presence of multiple ruthenium centers in the cage results in multiple Ru-III/II reduction events, with a cathodic shift of the first reduction relative to that of [Ru(bpy)(3)]Cl-2 (0.56 V vs 1.05 V). The ligand-centered reduction shifts anodically (-1.29 vs -1.64 V) versus the first bpy reduction observed in the parent [Ru(bpy)(3)]Cl-2. The photophysical properties are explained by the existence of two localized charge transfer states in the cage molecule: one that draws upon the bipyridine pi* orbitals and the other upon the 2,4,6-tris(4-pyridyl)-1,3,5-triazine pi* orbitals.