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Controlling single-molecule conductance through lateral coupling of π orbitals


In recent years, various single-molecule electronic components have been demonstrated1. However, it remains difficult to predict accurately the conductance of a single molecule and to control the lateral coupling between the π orbitals of the molecule and the orbitals of the electrodes attached to it. This lateral coupling is well known to cause broadening and shifting of the energy levels of the molecule; this, in turn, is expected to greatly modify the conductance of an electrode–molecule–electrode junction2,3,4,5,6. Here, we demonstrate a new method, based on lateral coupling, to mechanically and reversibly control the conductance of a single-molecule junction by mechanically modulating the angle between a single pentaphenylene molecule bridged between two metal electrodes. Changing the angle of the molecule from a highly tilted state to an orientation nearly perpendicular to the electrodes changes the conductance by an order of magnitude, which is in qualitative agreement with theoretical models of molecular π-orbital coupling to a metal electrode. The lateral coupling is also directly measured by applying a fast mechanical perturbation in the horizontal plane, thus ruling out changes in the contact geometry or molecular conformation as the source for the conductance change.

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Figure 1: Lateral coupling.
Figure 2: Break junction and blinking experiments on a pentaphenylene molecular junction.
Figure 3: Blink-and-pull experiments on a tetraphenyl junction.
Figure 4: Blink-and-pull experiments on a pentaphenylene junction.
Figure 5: Blinking experiments coupled with a.c. horizontal and vertical distance modulation.
Figure 6: Total lateral coupling magnitude.

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The authors acknowledge support from the Office of Basic Energy Sciences, US Department of Energy (grant DE-FG03-01ER45943). I.D.-P. thanks the EU International Outgoing Marie Curie Programme for financial support.

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N.J.T. conceived the transport experiment. I.D.-P., J.H. and T.H. conducted the experiments and analysed the data. K.M. supervised the design and synthesis of the molecule. Z.-S.W. and G.Z. synthesized the molecule.

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Correspondence to Gang Zhou, Klaus Müllen or Nongjian Tao.

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The authors declare no competing financial interests.

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Diez-Perez, I., Hihath, J., Hines, T. et al. Controlling single-molecule conductance through lateral coupling of π orbitals. Nature Nanotech 6, 226–231 (2011).

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