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){(mu-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 photo physical 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.