Issue 6, 2018

Gateway state-mediated, long-range tunnelling in molecular wires


If the factors controlling the decay in single-molecule electrical conductance G with molecular length L could be understood and controlled, then this would be a significant step forward in the design of high-conductance molecular wires. For a wide variety of molecules conducting by phase coherent tunnelling, conductance G decays with length following the relationship G = AeβL. It is widely accepted that the attenuation coefficient β is determined by the position of the Fermi energy of the electrodes relative to the energy of frontier orbitals of the molecular bridge, whereas the terminal anchor groups which bind to the molecule to the electrodes contribute to the pre-exponential factor A. We examine this premise for several series of molecules which contain a central conjugated moiety (phenyl, viologen or α-terthiophene) connected on either side to alkane chains of varying length, with each end terminated by thiol or thiomethyl anchor groups. In contrast with this expectation, we demonstrate both experimentally and theoretically that additional electronic states located on thiol anchor groups can significantly decrease the value of β, by giving rise to resonances close to EF through coupling to the bridge moiety. This interplay between the gateway states and their coupling to a central conjugated moiety in the molecular bridges creates a new design strategy for realising higher-transmission molecular wires by taking advantage of the electrode–molecule interface properties.

Graphical abstract: Gateway state-mediated, long-range tunnelling in molecular wires

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Article information

Article type
28 Sep 2017
29 Nov 2017
First published
29 Jan 2018
This article is Open Access
Creative Commons BY license

Nanoscale, 2018,10, 3060-3067

Gateway state-mediated, long-range tunnelling in molecular wires

S. Sangtarash, A. Vezzoli, H. Sadeghi, N. Ferri, H. M. O'Brien, I. Grace, L. Bouffier, S. J. Higgins, R. J. Nichols and C. J. Lambert, Nanoscale, 2018, 10, 3060 DOI: 10.1039/C7NR07243K

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