Photoexcitationof [Ru(tpy)(bpy)(-CN)Ru(py) 4 Cl] 2+ ([RuRu] 2+ ) at 387 nm results in the population of two 3 MLCT excited states of different symmetry that coexist in the nanosecond scale. Common to both states is an excited electron in a tpy-based orbital. Their configuration differs in the position of the hole. In one excited state, 3 MLCTz, the hole sits in an orbital parallel to the intermetallic axis allowing for a strong metal-metal electronic interaction. As a result, 3 MLCTz is highly delocalized over both metal centres and shows an intense photoinduced intervalence charge transfer (PIIVCT) NIR signature. In the other excited state, 3 MLCTxy, the hole is localized in an orbital perpendicular to the intermetallic axis and hence, significant intermetallic coupling is absent. This state shows no PIIVCT in the NIR and its spectrum is very similar to the one observed for the monometallic [Ru(tpy)(bpy)(CN)] + reference. Both 3 MLCT excited states have nanosecond lifetimes. The intervening energy barrier for a hole reconfiguration between the two different 3 MLCT excited states offers the opportunity to exploit wavefunctions of different symmetry before either the interconversion between them or the decay to the ground state is operative.

The picosecond excited state dynamics of [Ru(tpm)(bpy)(NCS)]+ (RubNCS+) and [Ru(tpm)(bpy)(CN)]+ (RubCN+) (tpm = tris(1-pyrazolyl)methane, bpy = 2,2′-bipyridine) reveal an intermediate MLCT excited state living in the 300 ps timescale.

Despite the large body of work on {Ru(bpy)} sensitizer fragments, the same attention has not been devoted to their {Ru(py)} analogues. In this context, we explored the donor-acceptor trans-[Ru(L){(μ-NC)Cr(CN)}], 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)} 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)} sensitizer fragments are as efficient as {Ru(bpy)} in short-range energy transfer scenarios.