Ferrocene-Terminated Oligourea Foldamer Monolayers

We have designed and synthesized two alpha-helicomimetic foldamers composed of six urea residues with terminal ferrocene and cysteamine moieties. The direction of the net dipole moment in these two compounds was opposite, and it was directed either toward the ferrocene moiety or cysteine. We have found that the direction of the dipole moment affects electrochemical behavior of oligourea monolayers deposited on a gold electrode. By employing in situ surface-enhanced infrared reflection-absorption spectroscopy, we were able to demonstrate that the electric field-induced dynamics of the molecules adsorbed on the electrode surface is determined by the specific distribution of the charge along the molecule, which results from the presence of a large dipole moment aligned with the molecular axis. We have also observed that the extent of molecular motion affects the kinetics of electron transfer between ferrocene redox sites and the electrode. This shows the importance of molecular dynamics in long-range electron transport mediated by molecular bridges.