Density Functional Theory Investigations of Ferrocene-Terminated Self-Assembled Monolayers: Electronic State Changes Induced by Electric Dipole Field of Coadsorbed Species

Ferrocene-terminated self-assembled monolayers (SAMs) have been widely studied in the past quarter century to reveal the electrochemical properties of chemically modified electrodes. It has been well-known that the formal potential of the system strongly depends on the local environment of the ferrocene moiety. Although electronic states of ferroceneterminated SAMs should directly affect the electrochemical properties, knowledge concerning electronic structures with respect to different local environment is very limited. In this study, we performed density functional theory calculations of ferrocene-terminated SAMs with different coadsorbed species to reveal the relationship between the electronic structures and the local environment of ferrocene moieties. Depending on the local electrostatic potential, density of states derived from the highest-occupied molecular orbital (HOMO) and its-vicinities (HOMO-1 and HOMO-2) of the ferrocene moiety were found to largely shift with respect to the electrode Fermi level up to 0.75 eV. This result leads to a novel strategy for designing sophisticated chemically modified electrodes where the electronic properties are electrostatically regulated by coadsorbed inert molecules.