Substituent-mediated quantum interference toward a giant single-molecule conductance variation

2021 ◽  
Author(s):  
Yi-Fan Zhou ◽  
Wen-Yan Chang ◽  
Jing-Zhe Chen ◽  
Jun-Ren Huang ◽  
Jia-Ying Fu ◽  
...  
Keyword(s):  
Single Molecule ◽  
Quantum Interference ◽  
High Performance ◽  
Substituent Effects ◽  
Molecular Junctions ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Transmission Coefficients ◽  
Order Of Magnitude ◽  
Promising Perspective

Abstract Quantum interference (QI) in single molecular junctions shows a promising perspective for realizing conceptual nanoelectronics. However, controlling and modulating the QI remains a big challenge. Herein, two-type substituents at different positions of meta-linked benzene, namely electron-donating methoxy (-OMe) and electron-withdrawing nitryl (-NO2), are designed and synthesized to investigate the substituent effects on QI. The calculated transmission coefficients T(E) indicates that -OMe and -NO2 could remove the antiresonance and destructive quantum interference (DQI)-induced transmission dips at position 2. -OMe could raise the antiresonance energy at position 4 while -NO2 groups removes the DQI features. For substituents at position 5, both of them are nonactive for tuning QI. The conductance measurements by scanning tunneling microscopy break junction (STM-BJ) show a good agreement with the theoretical prediction. More than two order of magnitude single-molecule conductance on/off ratio could be achieved at the different positions of -NO2 substituent groups at room temperature. The present work proves chemical substituents can be used for tuning QI features in single molecular junctions, which provides a feasible way toward realization of high-performance molecular devices.

Charge Transfer Complexation Boosts Molecular Conductance Through Fermi Level Pinning

2018 ◽  
Author(s):  
Kun Wang ◽  
Andrea Vezzoli ◽  
Iain Grace ◽  
Maeve McLaughlin ◽  
Richard Nichols ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Single Molecule ◽  
Quantum Interference ◽  
Transmission Function ◽  
Scanning Tunneling ◽  
Charge Transfer Complexes ◽  
Tunneling Microscopy ◽  
Quantum Interference Effect ◽  
Single Molecule Junctions ◽  
Charge Transfer Complexation

We have used scanning tunneling microscopy to create and study single molecule junctions with thioether-terminated oligothiophene molecules. We find that the conductance of these junctions increases upon formation of charge transfer complexes of the molecules with tetracyanoethene, and that the extent of the conductance increase is greater the longer is the oligothiophene, i.e. the lower is the conductance of the uncomplexed molecule in the junction. We use non-equilibrium Green's function transport calculations to explore the reasons for this theoretically, and find that new resonances appear in the transmission function, pinned close to the Fermi energy of the contacts, as a consequence of the charge transfer interaction. This is an example of a room temperature quantum interference effect, which in this case boosts junction conductance in contrast to earlier observations of QI that result in diminished conductance.<br>

Charge Transfer Complexation Boosts Molecular Conductance Through Fermi Level Pinning

2018 ◽  
Author(s):  
Kun Wang ◽  
Andrea Vezzoli ◽  
Iain Grace ◽  
Maeve McLaughlin ◽  
Richard Nichols ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Single Molecule ◽  
Quantum Interference ◽  
Transmission Function ◽  
Scanning Tunneling ◽  
Charge Transfer Complexes ◽  
Tunneling Microscopy ◽  
Quantum Interference Effect ◽  
Single Molecule Junctions ◽  
Charge Transfer Complexation

We have used scanning tunneling microscopy to create and study single molecule junctions with thioether-terminated oligothiophene molecules. We find that the conductance of these junctions increases upon formation of charge transfer complexes of the molecules with tetracyanoethene, and that the extent of the conductance increase is greater the longer is the oligothiophene, i.e. the lower is the conductance of the uncomplexed molecule in the junction. We use non-equilibrium Green's function transport calculations to explore the reasons for this theoretically, and find that new resonances appear in the transmission function, pinned close to the Fermi energy of the contacts, as a consequence of the charge transfer interaction. This is an example of a room temperature quantum interference effect, which in this case boosts junction conductance in contrast to earlier observations of QI that result in diminished conductance.<br>

scholarly journals Single-molecule level control of host-guest interactions in metallocycle-C60 complexes

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Jian-Hong Tang ◽  
Yueqi Li ◽  
Qingqing Wu ◽  
Zixiao Wang ◽  
Songjun Hou ◽  
...  
Keyword(s):  
Single Molecule ◽  
Guest Molecule ◽  
Scanning Tunneling ◽  
Level Control ◽  
Tunneling Microscopy ◽  
Central Importance ◽  
Single Molecule Level ◽  
Order Of Magnitude ◽  
Different Shapes ◽  
Mechanical Stretching

Abstract Host−guest interactions are of central importance in many biological and chemical processes. However, the investigation of the formation and decomplexation of host−guest systems at the single-molecule level has been a challenging task. Here we show that the single-molecule conductance of organoplatinum(II) metallocycle hosts can be enhanced by an order of magnitude by the incorporation of a C60 guest molecule. Mechanically stretching the metallocycle-C60 junction with a scanning tunneling microscopy break junction technique causes the release of the C60 guest from the metallocycle, and consequently the conductance switches back to the free-host level. Metallocycle hosts with different shapes and cavity sizes show different degrees of flexibility to accommodate the C60 guest in response to mechanical stretching. DFT calculations provide further insights into the electronic structures and charge transport properties of the molecular junctions based on metallocycles and the metallocycle-C60 complexes.

scholarly journals Mechanical single-molecule potentiometers with large switching factors from ortho-pentaphenylene foldamers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jinshi Li ◽  
Pingchuan Shen ◽  
Shijie Zhen ◽  
Chun Tang ◽  
Yiling Ye ◽  
...  
Keyword(s):  
Charge Transport ◽  
Single Molecule ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Helical Structures ◽  
Anchoring Groups ◽  
Molecular Conductance ◽  
And Control ◽  
Helical Molecules ◽  
Shed Light

AbstractMolecular potentiometers that can indicate displacement-conductance relationship, and predict and control molecular conductance are of significant importance but rarely developed. Herein, single-molecule potentiometers are designed based on ortho-pentaphenylene. The ortho-pentaphenylene derivatives with anchoring groups adopt multiple folded conformers and undergo conformational interconversion in solutions. Solvent-sensitive multiple conductance originating from different conformers is recorded by scanning tunneling microscopy break junction technique. These pseudo-elastic folded molecules can be stretched and compressed by mechanical force along with a variable conductance by up to two orders of magnitude, providing an impressively higher switching factor (114) than the reported values (ca. 1~25). The multichannel conductance governed by through-space and through-bond conducting pathways is rationalized as the charge transport mechanism for the folded ortho-pentaphenylene derivatives. These findings shed light on exploring robust single-molecule potentiometers based on helical structures, and are conducive to fundamental understanding of charge transport in higher-order helical molecules.

scholarly journals Photo-induced carbocation-enhanced charge transport in single-molecule junctions

2020 ◽  
Vol 11 (23) ◽  
pp. 6026-6030
Author(s):  
Zhongwu Bei ◽  
Yuan Huang ◽  
Yangwei Chen ◽  
Yiping Cao ◽  
Jin Li
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Charge Transport ◽  
Single Molecule ◽  
Scanning Tunneling ◽  
Break Junction ◽  
Tunneling Microscopy ◽  
Single Molecule Junctions

We report the first example of photo-induced carbocation-enhanced charge transport in triphenylmethane junctions using the scanning tunneling microscopy break junction (STM-BJ) technique.

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