Unusual Length Dependence of the Conductance in Cumulene Molecular Wires

Xu, Wenjun; Leary, Edmund; Hou, Songjun; Sangtarash, Sara; González, M. Teresa; Rubio‐Bollinger, Gabino; Wu, Qingqing; Sadeghi, Hatef; Tejerina, Lara; Christensen, Kirsten E.; Agraı̈t, Nicolás; Higgins, Simon J.; Lambert, Colin J.; Nichols, Richard J.; Anderson, Harry L.

doi:10.1002/ange.201901228

Cited by 26 publications

(33 citation statements)

References 47 publications

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“…Although less stable than polyynes, [9]cumulenes have been characterized, and functionalized [3]-and [5]cumulenes have been measured in single-molecule junction experiments. 13,[19][20] The single-molecule conductance of odd-n cumulenes is expected to be higher than that of equivalent polyynes due to the smaller bond-length alternation, which narrows the HOMO-LUMO gap. 55 ELECTRONIC STRUCTURE.…”

Section: Odd-n Cumulenic Carbon Wiresmentioning

confidence: 99%

“…Owing to the orientation of the end-groups, there is not much electronic communication through the p-systems of the molecule; the single-molecule conductance of a functionalized [2]cumulene (allene) was recently measured to be almost two orders of magnitude lower than that of the equivalent [3]cumulene. 19 However, we recently demonstrated that the electronic transmission through even-n cumulenes can be almost as high as that of the equivalent odd-n systems by splitting the helical frontier molecular orbitals using pyramidalized p-donor substituents. Strategies for manipulating the helical electronic structure of cumulenes using substituents is described in detail elsewhere.…”

Section: Even-n Cumulenic Carbon Wiresmentioning

confidence: 99%

“…The electron transport properties of several short molecular carbynes have been examined experimentally in single-molecule junctions for both polyynic and cumulenic molecular wires. [14][15][16][17][18][19][20] In single-molecule junctions the chemical structure of the isolated molecule is typically retained, and therefore the polyynic or cumulenic configuration of the molecular wire can be controlled by chemical design.…”

Section: Introductionmentioning

confidence: 99%

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Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

2020

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The one-dimensional carbon allotrope carbyne, a linear chain of sp-hybridized carbon atoms, is predicted to exist in a polyynic and a cumulenic structure. While molecular forms of carbyne have been extensively characterized, the structural nature is hard to determine for many linear carbon wires that are made in-situ during pulling experiments. Here, we show that cumulenes and polyynes have distinctively different low-bias conductance profiles under axial torsion. We analyze the change of the electronic structure, Landauer transmission, and ballistic current density of the three types of closed-shell molecular carbynes as a function of the torsion angle. Both polyynic, odd-carbon cumulenic, and even-carbon cumulenic carbon wires exhibit helical frontier molecular orbitals when the end-groups are not in a co-planar configuration. This helical conjugation effect gives rise to strong ring current patterns around the linear wires. Only the transmission of even-carbon polyynic wires follows the well-known cosine-squared law with axial torsion that is also seen in biphenyl-type systems. Notably, the transmission of even-carbon cumulenic carbon wires rises with axial torsion from co-planar towards perpendicular orientation of the end-groups. The three distinct transmission profiles of polyynes, odd-carbon cumulenes, and even-carbon cumulenes may allow for experimental identification of the structural nature of linear carbon wires. Their different electron transport properties under axial torsion furthermore underline that, in the molecular limit of carbyne, three different subclasses of linear carbon wires exist. File list (3)download file view on ChemRxiv torsion_chemrxiv3.pdf (6.17 MiB) download file view on ChemRxiv SI_chemrxiv3.pdf (9.24 MiB) download file view on ChemRxiv files.zip (21.38 MiB)

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Section: Odd-n Cumulenic Carbon Wiresmentioning

confidence: 99%

Section: Even-n Cumulenic Carbon Wiresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

2020

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Section: Odd-n Cumulenic Carbon Wiresmentioning

confidence: 99%

Three Distinct Torsion Profiles of Electronic Transmission Through Linear Carbon Wires

Garner

Bro-Jørgensen²,

Solomon³

2020

Preprint

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The one-dimensional carbon allotrope carbyne, a linear chain of sp-hybridized carbon atoms, is predicted to exist in a polyynic and a cumulenic structure. While molecular forms of carbyne have been extensively characterized, the structural nature is hard to determine for many linear carbon wires that are made in-situ during pulling experiments. Here, we show that cumulenes and polyynes have distinctively different low-bias conductance profiles under axial torsion. We analyze the change of the electronic structure, Landauer transmission, and ballistic current density of the three types of closed-shell molecular carbynes as a function of the torsion angle. Both polyynic, odd-carbon cumulenic, and even-carbon cumulenic carbon wires exhibit helical frontier molecular orbitals when the end-groups are not in a co-planar configuration. This helical conjugation effect gives rise to strong ring current patterns around the linear wires. Only the transmission of even-carbon polyynic wires follows the well-known cosine-squared law with axial torsion that is also seen in biphenyl-type systems. Notably, the transmission of even-carbon cumulenic carbon wires rises with axial torsion from co-planar towards perpendicular orientation of the end-groups. The three distinct transmission profiles of polyynes, odd-carbon cumulenes, and even-carbon cumulenes may allow for experimental identification of the structural nature of linear carbon wires. Their different electron transport properties under axial torsion furthermore underline that, in the molecular limit of carbyne, three different subclasses of linear carbon wires exist.

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“…The foundational experiments of Nongjian Tao 1 and subsequent work exploring charge transport through single molecules connected to two metallic electrodes 2 − 4 have led to the design of molecular-scale components such as switches, 4 − 6 rectifiers, 7 and highly conjugated molecular wires. 8 A more recent goal of this research is the design of thermoelectric materials 9 or devices 10 based on single molecules or self-assembled monolayers, 11 which can convert heat into electricity and contribute to the global challenge of green energy harvesting. Such organic materials and devices are potentially lightweight, flexible, environmentally friendly and cost-effective.…”

mentioning

confidence: 99%

Conformation and Quantum-Interference-Enhanced Thermoelectric Properties of Diphenyl Diketopyrrolopyrrole Derivatives

Almughathawi

Hou

et al. 2020

ACS Sens.

Self Cite

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Manipulating the connectivity of external electrodes to central rings of carbon-based molecules in single molecule junctions is an effective route to tune their thermoelectrical properties. Here we investigate the connectivity dependence of the thermoelectric properties of a series of thiophene-diketopyrrolopyrrole (DPP) derivative molecules using density functional theory and tight-binding modeling, combined with quantum transport theory. We find a significant dependence of electrical conductance on the connectivity of the two thiophene rings attached to the DPP core. Interestingly, for connectivities corresponding to constructive quantum interference (CQI), different isomers obtained by rotating the thiophene rings possess the same electrical conductance while those corresponding to destructive quantum interference (DQI) show huge conductance variations upon ring rotation. Furthermore, we find that DQI connectivity leads to enhanced Seebeck coefficients, which can reach 500–700 μV/K. After including the contribution to the thermal conductance from phonons, the full figure of merit ( ZT ) for the CQI molecules could reach 1.5 at room temperature and it would further increase to 2 when temperature elevates to 400 K. Finally, we demonstrate that doping with tetracyanoquinodimethane can change the sign of the Seebeck coefficients by forming a charge-transfer system with the DPP.

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Unusual Length Dependence of the Conductance in Cumulene Molecular Wires

Cited by 26 publications

References 47 publications

Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

Three Distinct Torsion Profiles of Electronic Transmission Through Linear Carbon Wires

Conformation and Quantum-Interference-Enhanced Thermoelectric Properties of Diphenyl Diketopyrrolopyrrole Derivatives

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