The electrochemical properties of the complexes were studied by cyclic voltammetry and differential pulse voltammetry in degassed acetonitrile. All complexes showed reversible oxidation waves with Eox ranging narrowly between 0.91 and 0.97 V vs SCE (see Figure and Table ). Most complexes exhibit very similar oxidation potentials to the parent IrPic (Eox = 0.96 V vs SCE). There is a relatively larger ca. 40 mV cathodic shift of the Eox for the three complexes that have trimethylsilyl groups at the 4-position of the phenyl ring: C4, C4N4, and C4N5. While the trimethylsilyl group has minimal electronic influence on an aryl ring (having small Hammet values of σm = -0.04 and σp = -0.07), it has previously been shown that the 4position of the phenyl ring of ppy-type ligands is the position most sensitive to electronic effects of substitution of emissive Ir(ppy)2(L) complexes, and suggests that substitution at the other positions on the ppy ligand will have a smaller impact on the state energies of the complex.