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

5 years ago

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

Yun Hee Jang, Yves Lansac, Taekhee Ryu

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.

Publisher URL: http://dx.doi.org/10.1021/acs.nanolett.7b00596

DOI: 10.1021/acs.nanolett.7b00596