A ruthenium
polypyridyl chromophore with electronically isolated
triarylamine substituents has been synthesized that models the role
of tyrosine in the electron transport chain in photosystem II. When
bound to the surface of a TiO<sub>2</sub> electrode, electron injection
from a Ru(II) Metal-to-Ligand Charge Transfer (MLCT) excited state
occurs from the complex to the electrode to give Ru(III). Subsequent
rapid electron transfer from the pendant triarylamine to Ru(III) occurs
with an observed rate constant of ∼10<sup>10</sup> s<sup>–1</sup>, which is limited by the rate of electron injection into the semiconductor.
Transfer of the oxidative equivalent away from the semiconductor surface
results in dramatically reduced rates of back electron transfer, and
a long-lived (τ = ∼165 μs) triarylamine radical
cation that has been used to oxidize hydroquinone to quinone in solution
