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We demonstrate that imidazole based π–π stacked dimers form strong and efficient conductance pathways in single-molecule junctions using the scanning-tunneling microscope-break junction (STM-BJ) technique and density functional theory-based calculations. We first characterize an imidazole-gold contact by measuring the conductance of imidazolyl-terminated alkanes ( im-N-im , N = 3–6). We show that the conductance of these alkanes decays exponentially with increasing length, indicating that the mechanism for electron transport is through tunneling or super-exchange. We also reveal that π–π stacked dimers can be formed between imidazoles and have better coupling than through-bond tunneling. These experimental results are rationalized by calculations of molecular junction transmission using non-equilibrium Green's function formalism. This study verifies the capability of imidazole as a Au-binding ligand to form stable single- and π-stacked molecule junctions at room temperature.
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Solvent-Mediated Modulation of the Au–S Bond in Dithiol Molecular Junctions
Gold-dithiol molecular junctions have been studied both experimentally and theoretically. However, the nature of the gold-thiolate bond as it relates to the solvent has been seldom investigated. It is known that solvents can impact the electronic structure of single molecule junctions, but the correlation between the solvent and dithiol-linked single-molecule junction conductance is not well understood. We study molecular junctions formed with thiol terminated phenylenes from both 1-chloronaphthalene and 1-bromonaphthalene solutions. We find that the most probable conductance and the distribution of conductances are both affected by the solvent. First-principles calculations show that junction conductance depends on the binding configurations (adatom, atop, bridge) of the thiolate on the Au surface as has been shown previously. More importantly, we find that brominated solvents can restrict the binding of thiols to specific Au sites. This mechanism offers new insight into the effects of the solvent environment on covalent bonding in molecular junctions.
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- PAR ID:
- 10512802
- Editor(s):
- NA
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Nano Letters
- Volume:
- 24
- Issue:
- 2
- ISSN:
- 1530-6984
- Page Range / eLocation ID:
- 703 to 707
- Subject(s) / Keyword(s):
- Single molecule measurements, Density Functional Theory, Scanning Tunneling Microscope-based Break Junction measurements, Thiol-gold bonding
- Format(s):
- Medium: X Size: N/A Other: N/A
- Size(s):
- N/A
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.nanolett.3c04058
