Shuttlecock-Shaped Molecular Rectifier: Asymmetric Electron
Transport Coupled with Controlled Molecular Motion

A fullerene derivative with five hydroxyphenyl groups attached around a pentagon, (4-HOC6H4)5HC60 (1), has
shown an asymmetric current−voltage (I−V) curve in a conducting atomic force microscopy experiment on gold. Such
molecular rectification has been ascribed to the asymmetric distribution of frontier molecular orbitals over its shuttlecock-shaped
structure. Our nonequilibrium Green’s function (NEGF) calculations based on density functional theory (DFT) indeed exhibit
an asymmetric I−V curve for 1 standing up between two Au(111) electrodes, but the resulting rectification ratio (RR ∼ 3) is
insufficient to explain the wide range of RR observed in experiments performed under a high bias voltage. Therefore, we
formulate a hypothesis that high RR (>10) may come from molecular orientation switching induced by a strong electric field
applied between two electrodes. Indeed, molecular dynamics simulations of a self-assembled monolayer of 1 on Au(111) show
that the orientation of 1 can be switched between standing-up and lying-on-the-side configurations in a manner to align its
molecular dipole moment with the direction of the applied electric field. The DFT−NEGF calculations taking into account such
field-induced reorientation between up and side configurations indeed yield RR of ∼13, which agrees well with the experimental
value obtained under a high bias voltage.