The relationship between charge transfer emission energies and redox potentials has been investigated for a large and diverse set of ruthenium diimine complexes. An alternative derivation of excited state redox potentials is developed, which relates them directly to the corresponding (observable) ground state potentials and allows them to be estimated when the 0-0’ emission energy is unknown. The difference between the excited state and corresponding ground state potentials, D, is shown to be approximately constant for complexes in which the emission and reduction processes involve "bipyridine-like" ligands, provided there are no strong specific solvent-solute interactions. Excited state redox potentials may also be obtained directly by using ligand electrochemical parameters, E(L)(L). E(L)(L(-)) values are calculated here for a number of reduced ligands.