Xu, Wenjun, Leary, Edmund, Sangtarash, Sara, Jirasek, Michael, Teresa Gonzalez, M, Christensen, Kirsten E, Abellan Vicente, Lydia, Agrait, Nicolas, Higgins, Simon J ORCID: 0000-0003-3518-9061, Nichols, Richard J
ORCID: 0000-0002-1446-8275 et al (show 2 more authors)
(2021)
A Peierls Transition in Long Polymethine Molecular Wires: Evolution of Molecular Geometry and Single-Molecule Conductance.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 143 (48).
pp. 20472-20481.
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Wenjun-Harry Anderson- Peierls transitions JACS-rev_ms_Nov21.pdf - Author Accepted Manuscript Download (10MB) | Preview |
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Abstract
Molecules capable of mediating charge transport over several nanometers with minimal decay in conductance have fundamental and technological implications. Polymethine cyanine dyes are fascinating molecular wires because up to a critical length, they have no bond-length alternation (BLA) and their electronic structure resembles a one-dimensional free-electron gas. Beyond this threshold, they undergo a symmetry-breaking Peierls transition, which increases the HOMO-LUMO gap. We have investigated cationic cyanines with central polymethine chains of 5-13 carbon atoms (<b>Cy3</b><sup><b>+</b></sup><b>-Cy11</b><sup><b>+</b></sup>). The absorption spectra and crystal structures show that symmetry breaking is sensitive to the polarity of the medium and the size of the counterion. X-ray crystallography reveals that <b>Cy9·PF</b><sub><b>6</b></sub> and <b>Cy11·B(C</b><sub><b>6</b></sub><b>F</b><sub><b>5</b></sub><b>)</b><sub><b>4</b></sub> are Peierls distorted, with high BLA at one end of the π-system, away from the partially delocalized positive charge. This pattern of BLA distribution resembles that of solitons in polyacetylene. The single-molecule conductance is essentially independent of molecular length for the polymethine salts of <b>Cy3</b><sup><b>+</b></sup><b>-Cy11</b><sup><b>+</b></sup> with the large B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub><sup>-</sup> counterion, but with the PF<sub>6</sub><sup>-</sup> counterion, the conductance decreases for the longer molecules, <b>Cy7</b><sup><b>+</b></sup><b>-Cy11</b><sup><b>+</b></sup>, because this smaller anion polarizes the π-system, inducing a symmetry-breaking transition. At higher bias (0.9 V), the conductance of the shorter chains, <b>Cy3</b><sup><b>+</b></sup><b>-Cy7</b><sup><b>+</b></sup>, increases with length (negative attenuation factor, β = -1.6 nm<sup>-1</sup>), but the conductance still drops in <b>Cy9</b><sup><b>+</b></sup> and <b>Cy11</b><sup><b>+</b></sup> with the small polarizing PF<sub>6</sub><sup>-</sup> counteranion.
Item Type: | Article |
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Divisions: | Faculty of Science and Engineering > School of Physical Sciences |
Depositing User: | Symplectic Admin |
Date Deposited: | 31 Jan 2022 08:48 |
Last Modified: | 18 Jan 2023 21:14 |
DOI: | 10.1021/jacs.1c10747 |
Related URLs: | |
URI: | https://livrepository.liverpool.ac.uk/id/eprint/3147860 |