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Correlations between Molecular Structure and Single-Junction Conductance: A Case Study with Oligo(phenylene-ethynylene)-Type Wires

Kaliginedi, Veerabhadrarao and Moreno-Garcia, Pavel and Valkenier, Hennie and Hong, Wenjing and Garcia-Suarez, Victor M. and Buiter, Petra and Otten, Jelmer L. H. and Hummelen, Jan C. and Lambert, Colin J. and Wandlowski, Thomas (2012) Correlations between Molecular Structure and Single-Junction Conductance: A Case Study with Oligo(phenylene-ethynylene)-Type Wires. Journal of the American Chemical Society, 134 (11). pp. 5262-5275. ISSN 0002-7863

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Abstract

The charge transport characteristics of 11 tailor-made dithiol-terminated oligo(phenylene-ethynylene) (OPE)-type molecules attached to two gold electrodes were studied at a solid/liquid interface in a combined approach using an STM break junction (STM-BJ) and a mechanically controlled break junction (MCBJ) setup. We designed and characterized 11 structurally distinct dithiol-terminated OPE-type molecules with varied length and HOMO/LUMO energy. Increase of the molecular length and/or of the HOMO-LUMO gap leads to a decrease of the single-junction conductance of the linearly conjugate acenes. The experimental data and simulations suggest a nonresonant tunneling mechanism involving hole transport through the molecular HOMO, with a decay constant beta = 3.4 +/- 0.1 nm(-1) and a contact resistance R-c = 40 k Omega per Au-S bond. The introduction of a cross-conjugated anthraquinone or a dihydroanthracene central unit results in lower conductance values, which are attributed to a destructive quantum interference phenomenon for the former and a broken pi-conjugation for the latter. The statistical analysis of conductance-distance and current-voltage traces revealed details of evolution and breaking of molecular junctions. In particular, we explored the effect of stretching rate and junction stability. We compare our experimental results with DFT calculations using the ab initio code SMEAGOL and discuss how the structure of the molecular wires affects the conductance values.

Item Type: Article
Journal or Publication Title: Journal of the American Chemical Society
Subjects: Q Science > QC Physics
Departments: Faculty of Science and Technology > Physics
ID Code: 57839
Deposited By: ep_importer_pure
Deposited On: 28 Aug 2012 13:34
Refereed?: Yes
Published?: Published
Last Modified: 10 Apr 2014 00:03
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/57839

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