Shuttlecock-Shaped Molecular Rectifier: Asymmetric Electron Transport Coupled with Controlled Molecular Motion
T Ryu and Y Lansac and YH Jang, NANO LETTERS, 17, 4061-4066 (2017).
A fullerene derivative with five hydroxyphenyl groups attached around a pentagon, (4-HOC6H4)(5)HC60 (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 similar to 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 similar to 13, which agrees well with the experimental value obtained under a high bias voltage.
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