Dynamics of electron transfer reactions in ruthenium-based donor-chromophore-acceptor complexes involving phenothiazine-type donors

Abstract

A series of electron donating groups were synthesized to study the effect of driving force on the electron transfer between the donor and a photoexcited trisbipyridineruthenium (II) chromophore. The driving force for the electron transfer reaction is directly related to the oxidation potential of the donor. The findings can be understood in terms of a combination of driving force and a π-π interaction between the donor and the chromophore. The π-π interaction was investigated to determine its role in the electron transfer reaction. To this end, a series of bipyridine-like ligands were used to make chromophores that either favored or hindered the π-π interaction. The existence of the π-π interaction was shown by spectroscopy and NMR studies. The electron transfer rates for the ligand series reflect both the importance of the π-π interaction and driving force in these systems (ligand substitution affects the emission energy for a chromophore which in turn affects the driving force for the electron transfer reaction). The effect of the π-π interaction on the electron transfers in donor-chromophore-acceptor complexes was investigated in bimolecular quenching experiments between donor and chromophore-acceptor complexes. The results can be understood in terms of a scheme where a ground state π-π interaction between the donor and the chromophore is the primary mode of electron transfer in these systems. The π-π interaction is also used to explain the high quantum efficiency to the charge-separated state, where both the donor and the acceptor have undergone electron transfers with the chromophore.