Shuttlecock-Shaped Pentaarylfullerenes Self-Assembled on Au: Molecular Dynamics Simulation of a Molecular Rectifier

A shuttlecock-shaped fullerene derivative with five hydroxyphenyl functional groups at the bottom of C-60 has been known to exhibit a rectification behavior when self-assembled between gold electrodes. Since the common feature of molecular rectifiers, a spatial separation between the donor and the acceptor, is not exhibited in this compound, we formulate a hypothesis that its rectification could be related with a structural transition of its self-assembled monolayer (SAM) on gold. As the first step to confirm this hypothesis, we performed molecular dynamics (MD) simulations on its SAM on the Au(111) surface after a new force field (FF) is developed and validated against various properties experimentally measured on its component systems such as C-60, benzene, phenol, gold, and their combinations. The MD simulations with the final FF indeed support two types of SAM with different molecular orientations. The SAM is more stable when the molecular principal axis (which coincides with the dipolar axis) is parallel to the surface than when it is perpendicular to the surface, but the electric field from the top gate electrode could stabilize the latter and switch the orientation, partially supporting our hypothesis.