Turning the Tap: Conformational Control of Quantum Interference to Modulate Single‐Molecule Conductance

Jiang, Feng; Trupp, Douglas I.; Algethami, Norah; Zheng, Honghua; He, Wenxiang; Alqorashi, Afaf; Zhu, Chenxu; Tang, Chun; Li, Ruihao; Liu, Junyang; Sadeghi, Hatef; Shi, Jia; Davidson, Ross J.; Korb, Marcus; Sobolev, Alexandre N.; Naher, Masnun; Sangtarash, Sara; Low, Paul J.; Hong, Wenjing; Lambert, Colin J.

doi:10.1002/ange.201909461

Cited by 25 publications

(28 citation statements)

References 53 publications

(31 reference statements)

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“…NEGF-DFT places the Fermi energy (EF) on the edge of the LUMO peak, but DFT is wellknown to underestimate the HOMO-LUMO gap and often misplaces EF within that gap. 31 Instead, both orbital symmetry 32 and current-voltage measurements 33 suggest that the BT linker group leads to HOMO-mediated transport in the OPV3-2BT-X series. This assignment is also supported by the fact that the ordering of transmission functions along the edge of the LUMO-peak (Figure 3b) is in stark disagreement with our experimental results.…”

Section: Resultsmentioning

confidence: 99%

Correlated Energy-Level Alignment Effects Determine Substituent-Tuned Single-Molecule Conductance

Ivie

Bamberger

Parida

et al. 2021

ACS Appl. Mater. Interfaces

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The rational design of single molecule electrical components requires a deep and predictive understanding of structure-function relationships. Here we explore the relationship between chemical substituents and the conductance of metal-single molecule-metal junctions, using functionalized oligophenylenevinylenes as a model system. Using a combination of mechanically controlled break-junction experiments and various levels of theory including non-equilibrium Green's functions, we demonstrate that the connection between gas-phase molecular electronic structure and in-junction molecular conductance is complicated by the involvement of multiple mutually correlated and opposing effects that contribute to energy level alignment in the junction. We propose that these opposing correlations represent powerful new "design principles," because their physical origins make them broadly applicable, and they are capable of predicting the direction and relative magnitude of observed conductance trends. In particular, we show that they are consistent with the observed conductance variability not just within our own experimental results, but also within disparate molecular series reported in literature and, crucially, with the trend in variability across these molecular series, which previous simple models fail to explain. The design principles introduced here can therefore aid in both screening and suggesting novel design strategies for maximizing conductance tunability in single-molecule systems.

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Section: Resultsmentioning

confidence: 99%

Correlated Energy-Level Alignment Effects Determine Substituent-Tuned Single-Molecule Conductance

Ivie

Bamberger

Parida

et al. 2021

ACS Appl. Mater. Interfaces

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“…This is exemplified in Figure 1 Substituent effects are well-established for destructive quantum interference effects in conjugated molecules. [28][29][30][31] The destructive p-interference effect can be systematically manipulated depending on the electron donating or withdrawing character of the substituent. [32][33][34][35][36][37][38][39][40] Here, we examine the substituent effect on the electronic transmission of methylthiomethyl-functionalized bicyclo[2.2.2]octane (C222), bicyclo[2.2.2]octasilane, and bicyclo[2.2.2]octagermane (Ge222).…”

Section: Manuscriptmentioning

confidence: 99%

Substituent Control of σ-interference Effects in the Transmission of Saturated Molecules

Garner

Koerstz

Jensen

et al. 2021

Preprint

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The single-molecule conductance of saturated molecules can potentially be fully suppressed by destructive quantum interference in their σ-system. However, only few molecules with σ-interference have been identified and the structure-property relationship remains to be elucidated. Here, we explore the role of substituents in modulating the electronic transmission of saturated molecules. In functionalized bicyclo[2.2.2]octanes, the transmission is suppressed by σ- interference when fluorine substituents are applied. For bicyclo[2.2.2]octasilane and - octagermanes the transmission is suppressed when carbon-based substituents are used, and such molecules are likely to be highly insulating. For the carbon-based substituents we find a strong correlation between the appropriate Hammett constants and the transmission. The substituent effect enables systematic optimization of the insulating properties of saturated molecular cores.

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“…14,[24][25][26][27] The conductance difference between meta-and paralinked benzenes is therefore larger in longer molecules when s-transport is naturally suppressed due to faster decay with length. [28][29][30][31][32][33][34][35][36][37][38] An optimal insulating/dielectric molecule will, however, deliver the lowest possible conductance with the shortest possible length. We consider the para-case the archetypical p-conductor and the meta-case the archetypical pinsulator as shown in Scheme 1.…”

Section: Toc Graphicsmentioning

confidence: 99%

Simultaneous Suppression of pi- and sigma- Transmission in pi-Conjugated Molecules

Gc²

2020

Preprint

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<div><div><div><p>Molecular dielectric materials require ostensibly conflicting requirements of high polarizability and low conductivity. As previous efforts towards molecular insulators focused on saturated molecules, it remains an open question whether pi- and sigma-transport can be simultaneously suppressed in conjugated systems. Here, we demonstrate that there are conjugated molecules where the sigma-transmission is suppressed by destructive sigma-interference, while the pi-transmission can be suppressed by a localized disruption of conjugation. Using density functional theory, we study the Landauer transmission and ballistic current density, which allow us to determine how the transmission is affected by various structural changes in the molecule. We find that in para-linked oligophenyl rings the sigma-transmission can be suppressed by changing the remaining hydrogens to methyl groups due to the inherent gauche-like structure of the carbon backbone within a benzene ring, similar to what was previously seen in saturated systems. At the same time, the methyl groups fulfil a dual purpose as they modulate the twist angle between neighboring phenyl rings. When neighboring rings are orthogonal to each other, the transmission through both pi- and sigma-systems is effectively suppressed. Alternatively, breaking conjugation in a single phenyl ring by saturating two carbons atoms with two methyl substituents on each carbon, results in suppressed pi- and sigma-transport independent of dihedral angle. These two strategies demonstrate that methyl-substituted oligophenyls are promising candidates for the development of molecular dielectric materials.</p></div></div></div>

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Turning the Tap: Conformational Control of Quantum Interference to Modulate Single‐Molecule Conductance

Cited by 25 publications

References 53 publications

Correlated Energy-Level Alignment Effects Determine Substituent-Tuned Single-Molecule Conductance

Correlated Energy-Level Alignment Effects Determine Substituent-Tuned Single-Molecule Conductance

Substituent Control of σ-interference Effects in the Transmission of Saturated Molecules

Simultaneous Suppression of pi- and sigma- Transmission in pi-Conjugated Molecules

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