Electronic Energy Transduction from {Ru(py)₄} Chromophores to Cr(III) Luminophores

Despite the large body of work on {Ru(bpy) 2 } sensitizer fragments, the same attention has not been devoted to their {Ru(py) 4 } analogues. In this context, we explored the donor–acceptor trans -[Ru(L) 4 {(μ-NC)Cr(CN) 5 } 2 ] 4–, where L = pyridine, 4-methoxypyridine, 4-dimethylaminopyridine. We report on the synthesis and the crystal structure as well as the electrochemical, spectroscopical, and photophysical properties of these trimetallic complexes, including transient absorption measurements. We observed emission from chromium-centered d–d states upon illuminating into either MLCT or MM′CT absorptions of {Ru(L) 4 } or {Ru-Cr}, respectively. The underlying energy transfer is as fast as 600 fs with quantum efficiencies ranging from 10% to 100%. These results document that {Ru(py) 4 } sensitizer fragments are as efficient as {Ru(bpy) 2 } in short-range energy transfer scenarios.