Newly synthesized mixed-valence dimers made up of two oxo-centered, tri-ruthenium clusters and one Zinc (II)-5-(4-pyridyl)-10,15,20-triphenylporphyrin ancillary ligand provide novel systems capable of undergoing light-induced, intramolecular electron transfer. Utilizing the ancillary ligand opposite the porphyrin (L=4-dimethylaminopyridine, pyridine, or 4-cyanopyridine), the electronic environment across the singly reduced inorganic system can be finely tuned. The effect of this fine-tuning has been characterized electrochemically by two sequential single electron reductions occurring with deltaE >300mV. This energy difference can be related to the electronic coupling HAB between the triruthenium clusers and identifies L= 4-dmap to be the most stable singly reduced dimer. Singly reduced systems were generated via chemical reduction and characterized by their coalesced carbonyl lineshapes in the vibrational spectrum and two intervalence charge transfer (IVCT) bands in the near-IR. Analogous symmetric dimers show identical trends to those observed in the new dimers, specially increased coalescence is observed in the system with increased electron density on the ruthenium dimer (4-dmap) and diverging IVCT bands appear as the ground state potential energy surface adjusts to shift the metal-to-bridge to higher energy and the metal-to-metal to lower energy. In these systems the high-energy singlet excited-state of the porphyrin provides sufficient energy for electron injection from the photoexcitable ligand onto the pyrazine-bridged dimer, as determined using the Rehm-Weller equation to estimate deltaG values of <-0.5 eV for all systems. Intramolecular electron transfer was demonstrated under steady-state photolysis, in the presence of a sacrificial donor, by observing the growth of the near-IR IVCT bands. These systems have also been studied with ultrafast transient absorption spectroscopy, with initial results confirming porphyrin oxidation followed by relaxation to a vibrationally excited ground state.

Light-induced, intramolecular electron transfer resulting in highly coupled mixed-valence oxo-centered triruthenium dimers

248th National Meeting (2014)

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