Comparative Studies of Photoelectron Spectroscopy and Voltammetry of Ferrocene-Terminated Self-Assembled Monolayers Possessing Different Electron-Donating Abilities

The relationship between the oxidation potential determined by electrochemical measurements and the ionization energies measured by gas-phase ultraviolet photoelectron spectroscopy (UPS) has long been a focus of research of various groups. The focus of this study is to reveal such a correlation for redox molecules, which are chemically attached to metal electrodes. X-ray photoelectron spectroscopy, UPS, and cyclic voltammetry were performed for three types of ferrocene-terminated self-assembled monolayers possessing different electron-donating abilities. The results of these experiments indicate a linear relation with a slope of similar to 0.7 between the UPS-derived energy of the highest occupied molecular orbital (HOMO) and the electrochemical oxidation potential. This indicates that the HOMO energy can be used to determine the oxidation potential of chemically modified electrodes.