Permethylation Introduces Destructive Quantum Interference in Saturated Silanes

Garner, Marc H.; Li, Haixing; Neupane, Madhav Prasad; Zou, Qi; Liu, Taifeng; Su, Timothy A.; Shangguan, Zhichun; Paley, Daniel W.; Ng, Fay; Xiao, Shengxiong; Nuckolls, Colin; Venkataraman, Latha; Solomon, Gemma C.

doi:10.1021/jacs.9b06965

Cited by 42 publications

(71 citation statements)

References 61 publications

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“…This ad-atom serves as the attachment point to the SMe anchor units. In line with the geometrical data from previous work, 43,44 the Au-S distance was set to 2.45 Å, the Me-S-Au angle was set to 100°, and the C(Ph)-S-Me angle was set to 110°. The dihedral angle between the S-Au bond and the plane of the adjacent phenyl groups was set to 0°, so that disproportionate through-space coupling contributions between the contacts in the latter junction could be avoided.…”

Section: Transport Calculationsmentioning

confidence: 99%

Single-molecule switching via controlled tautomerization at room temperature

Hong¹,

Tang²,

Stuyver³

et al. 2020

Preprint

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The control of chemical reactivity at the single-molecule scale offers a unique opportunity for the design and fabrication of advanced nanodevices.1-3 As a prototypical reaction, tautomerization has been extensively explored as a promising tool for manipulating the single-molecule conductance of tetrapyrrole macrocycles absorbed on a surface.4-8 However, the resulting molecular devices were determined to undergo dynamic, spontaneous interconversions even under cryogenic conditions, so that control of tautomeric switching between well-defined and specific states remains challenging. Here, we report the design of a reversible single-molecule switch based on an enol-keto tautomerization reaction, which demonstrates controllable bistability and inhibits spontaneous interconversion even at room temperature. Such control is achieved by modulating the potential energy surface (PES) through a bias-triggered charge injection process. Our results reveal that the device operates through switching between two distinct redox-related PESs with opposite thermodynamic driving forces, i.e., one exhibits strong preference for the conducting enol form, while the other exhibits a preference for the insulating keto form. The described switching mechanism constitutes a promising approach to achieve robust switching devices at the single-molecule scale.

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Section: Transport Calculationsmentioning

confidence: 99%

Single-molecule switching via controlled tautomerization at room temperature

Hong¹,

Tang²,

Stuyver³

et al. 2020

Preprint

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show abstract

“…We and others recently uncovered chemical design rules for suppression of the stransmission in saturated molecules by destructive quantum interference. 14,[39][40][41] The sinterference effect can appear when there is a gauche defect in the molecular backbone, i.e., a dihedral angle of approximately 60° or less. Furthermore, the suppression is strongest in methyl-substituted species (as opposed to all substituents being hydrogen).…”

Section: Scheme 1 Transport Properties Of Organic Molecular Wiresmentioning

confidence: 99%

“…41 Therefore, the interference effect is clearest in the single-molecule conductance of saturated silanes that are generally permethylated, though it is also significant in alkanes. [41][42][43][44][45] By considering transalkanes the archetypical s-conductor and gauche-alkanes the archetypical s-insulator, we deduce from Scheme 1 that the structural requirements for pand s-interference appear to be mutually exclusive. The s-path through meta-benzene is structurally akin to that of the transalkane, and the s-path of para-benzene to that of the gauche-alkane.…”

Section: Scheme 1 Transport Properties Of Organic Molecular Wiresmentioning

confidence: 99%

“…This behavior upon substitution is similar to that we have recently demonstrated in cyclic and bicyclic silanes and alkanes. 14,41 The appearance of two antiresonances near the Fermi energy is predicted by the Hückel-type Ladder C model (see Supporting Information part C), but is usually not seen in DFT calculations. 39,[66][67] We note here that crystal structures obtained on similar biphenyl molecules found the dihedral angles for the hydrogen substituted system to be 36.4° while the methylated system was 89°.…”

Section: Scheme 1 Transport Properties Of Organic Molecular Wiresmentioning

confidence: 99%

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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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“…3 This effect has been demonstrated in a range of p-conjugated organic molecules [4][5][6][7][8] and in saturated s-conjugated silanes. [9][10][11][12] Saturated molecules with destructive interference in the s-system have particularly low conductance, as there is no p-channel and transmission through the s-channel is suppressed. [13][14][15][16][17] This opens a potential avenue for using molecules with destructive s-interference as molecular insulators.…”

Section: Introductionmentioning

confidence: 99%