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.