Electronic Conductance and Thermopower of Cross-Conjugated and Skipped-Conjugated Molecules in Single-Molecule Junctions

Salthouse, Rebecca J.; Hurtado-Gallego, Juan; Grace, Iain M.; Davidson, Ross; Alshammari, Ohud; Agraït, Nicolás; Lambert, Colin J.; Bryce, Martin R.

Abstract

We report a combined experimental and theoretical study of a series of thiomethyl (SMe) anchored cross-conjugated molecules featuring an acyclic central bridging ketone and their analogous skipped-conjugated alcohol derivatives. Studies of these molecules in a gold|single-molecule|gold junction using scanning tunneling microscopy-break junction techniques reveal a similar conductance (G) value for both the cross-conjugated molecules and their skipped-conjugated partners. Theoretical studies based on density functional theory of the molecules in their optimum geometries in the junction reveal the reason for this similarity in conductance, as the predicted conductance for the alcohol series of compounds varies more with the tilt angle. Thermopower measurements reveal a higher Seebeck coefficient (S) for the cross-conjugated ketone molecules relative to the alcohol derivatives, with a particularly high S for the biphenyl derivative 3a (−15.6 μV/K), an increase of threefold compared to its alcohol analog. The predicted behavior of the quantum interference (QI) in this series of cross-conjugated molecules is found to be constructive, though the appearance of a destructive QI feature for 3a is due to the degeneracy of the HOMO orbital and may explain the enhancement of the value of S for this molecule.

Citation

Salthouse, R. J., Hurtado-Gallego, J., Grace, I. M., Davidson, R., Alshammari, O., Agraït, N., …Bryce, M. R. (2023). Electronic Conductance and Thermopower of Cross-Conjugated and Skipped-Conjugated Molecules in Single-Molecule Junctions. Journal of Physical Chemistry C, 127(28), 13751-13758. https://doi.org/10.1021/acs.jpcc.3c00742

• Journal Article Type: Article
• Acceptance Date: Jun 22, 2023
• Online Publication Date: Jul 6, 2023
• Publication Date: Jul 20, 2023
• Deposit Date: Aug 16, 2023
• Publicly Available Date: Aug 16, 2023
• Journal: The Journal of Physical Chemistry C
• Print ISSN: 1932-7447
• Electronic ISSN: 1932-7455
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 127
• Issue: 28
• Pages: 13751-13758
• DOI: https://doi.org/10.1021/acs.jpcc.3c00742
• Keywords: Surfaces, Coatings and Films; Physical and Theoretical Chemistry; General Energy; Electronic, Optical and Magnetic Materials
• Public URL: https://durham-repository.worktribe.com/output/1719749