Influence of Donor‐Acceptor Interactions on MLCT Hole Reconfiguration in {Ru(bpy)} Chromophores

In MLCT chromophores, internal conversion (IC) in the form of hole reconfiguration pathways (HR) is a major source of dissipation of the absorbed photon energy. Therefore, it is desirable to minimize their impact in energy conversion schemes by slowing them down. According to previous findings on {Ru(bpy)} chromophores, donor‐acceptor interactions between the Ru ion and the ligand scaffold might allow to control HR/IC rates. Here, a series of [Ru(tpm)(bpy)(R‐py)]2+ chromophores, where tpm is tris(1‐pyrazolyl)methane, bpy is 2,2’‐bipyridine and R‐py is a 4‐substituted pyridine, were prepared and fully characterized employing electrochemistry, spectroelectrochemistry, steady‐state absorption/emission spectroscopy and electronic structure computations based on DFT/TD‐DFT. Their excited‐state decay was monitored using nanosecond and femtosecond transient absorption spectroscopy. HR/IC lifetimes as slow as 568 ps were obtained in DMSO at room temperature, twice as slow as in the reference species [Ru(tpm)(bpy)(NCS)]+. Excited state dynamics of metal‐to‐ligand charge transfer (MLCT) states have been explored in model ruthenium polypyridines. Substitution of ancillary ligands with electron‐donor groups decelerates internal conversion by means of hole reconfiguration, from high‐energy MLCT to the lowest‐energy MLCT, to 600 ps. This is promising in the design of strategies to extract the energy of high‐energy excited states before dissipation.