A highly efficient mechanism for the regeneration of the cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II) sensitizing dye (N3) by I(-) in acetonitrile has been identified by using molecular dynamics simulation based on density functional theory. Barrier-free complex formation of the oxidized dye with both I(-) and , and facile dissociation of and from the reduced dye are key steps in this process. In situ vibrational spectroscopy confirms the reversible binding of I(2) to the thiocyanate group. Additionally, simulations of the electrolyte near the interface suggest that acetonitrile is able to cover the (101) surface of anatase with a passivating layer that inhibits direct contact of the redox mediator with the oxide, and that the solvent structure specifically enhances the concentration of I(-) at a distance which further favors rapid dye regeneration.