Electron Transfer in Metal−Molecule−Metal Junction Composed of Self-Assembled Monolayers of Helical Peptides Carrying Redox-Active Ferrocene Units

Electronic properties of three kinds of helical peptides with or without redox-active ferrocene units were investigated by using scanning tunneling microscopy under ultrahigh vacuum. The currents through the helical peptides carrying ferrocene units at the molecular terminals became significantly larger than that through a reference peptide without any ferrocene units. On the other hand, ferrocene units in the middle of the peptide chain did not affect the current−voltage characteristics. These results indicate that the ferrocene units near the metal electrode should play an important role for efficient electron transfer between the metal and the peptide molecules, which process is one of the rate-determining steps for characterizing molecular conductance in metal−molecule−metal junction.