Heteroatom-Induced Molecular Asymmetry Tunes Quantum Interference in Charge Transport through Single-Molecule Junctions (original) (raw)
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Angewandte Chemie International Edition, 2019
Together with the more intuitive and commonly recognized conductance mechanisms of charge-hopping and tunneling,q uantum-interference (QI) phenomena have been identified as important factors affecting charge transport through molecules.C onsequently,e stablishing simple and flexible molecular-design strategies to understand, control, and exploit QI in molecular junctions poses an exciting challenge.H ere we demonstrate that destructive quantum interference (DQI) in meta-substituted phenylene ethylenetype oligomers (m-OPE) can be tuned by changing the position and conformation of methoxy (OMe) substituents at the central phenylene ring. These substituents play the role of molecularscale taps,w hich can be switched on or off to control the current flowt hrough am olecule.O ur experimental results conclusively verify recently postulated magic-ratio and orbitalproduct rules,a nd highlight an ovel chemical design strategy for tuning and gating DQI features to create single-molecule devices with desirable electronic functions.
The Relation between Structure and Quantum Interference in Single Molecule Junctions
Nano Letters, 2010
Quantum interference (QI) of electron pathways has recently attracted increased interest as an enabling tool for singlemolecule electronic devices. Although various molecular systems have been shown to exhibit QI effects and a number of methods have been proposed for its analysis, simple guidelines linking the molecular structure to QI effects in the phase-coherent transport regime have until now been lacking. In the present work we demonstrate that QI in aromatic molecules is intimately related to the topology of the molecule's π system and establish a simple graphical scheme to predict the existence of QI-induced transmission antiresonances. The generality of the scheme, which is exact for a certain class of tight-binding models, is proved by a comparison to first-principles transport calculations for 10 different configurations of anthraquinone as well as a set of cross-conjugated molecular wires.
A quantum circuit rule for interference effects in single-molecule electrical junctions
Nature Communications, 2015
A quantum circuit rule for combining quantum interference effects in the conductive properties of oligo(phenyleneethynylene) (OPE)-type molecules possessing three aromatic rings was investigated both experimentally and theoretically. Molecules were of the type X-Y-X, where X represents pyridyl anchors with para (p), meta (m) or ortho (o) connectivities and Y represents a phenyl ring with p and m connectivities. The conductances G XmX (G XpX ) of molecules of the form X-m-X (X-p-X), with meta (para) connections in the central ring, were predominantly lower (higher), irrespective of the meta, para or ortho nature of the anchor groups X, demonstrating that conductance is dominated by the nature of quantum interference in the central ring Y. The single-molecule conductances were found to satisfy the quantum circuit rule G ppp /G pmp ¼ G mpm /G mmm . This demonstrates that the contribution to the conductance from the central ring is independent of the para versus meta nature of the anchor groups.
Tuning Charge Transport Properties of Asymmetric Molecular Junctions
The Journal of Physical Chemistry C
Charge transport characteristics of asymmetric molecules containing a 9,9'-spirobifluorene platform coupled covalently to a phenylene ethynylene linker capped with either a thiol or a nitrile end group are investigated by break junction techniques. It is shown that the platform provides very good electronic coupling with metallic leads and the differences in the charge transport depend solely on the type of the anchoring group at the opposite end of the molecule. The SH-terminated molecule has one order of magnitude higher conductance compared to CN-terminated one and the charge transport path depends on the end group utilized. By a combined experimental break junction techniques and theoretical DFT calculations, it was demonstrated that in molecules containing SH-terminated phenylene ethynylene wire attached to the 9,9'-spirobifluorene platform the charge is transported through fluorene unit and covalently coupled phenylene ethynylene linker. For CN-terminated molecules the charge is transported through the thiolate termini of the 9,9'-spirobifluorene tripod. These studies demonstrate the potential of spirobifluorene platform for the bottom-up approach to molecular architectures by its immobilization with all three thiol groups to one of the electrodes without compromising charge transport via the conjugated backbone.
Gating of Quantum Interference in Molecular Junctions by Heteroatom Substitution
Angewandte Chemie (International ed. in English), 2017
To guide the choice of future synthetic targets for single-molecule electronics, qualitative design rules are needed, which describe the effect of modifying chemical structure. Here the effect of heteroatom substitution on destructive quantum interference (QI) in single-molecule junctions is, for the first time experimentally addressed by investigating the conductance change when a "parent" meta-phenylene ethylene-type oligomer (m-OPE) is modified to yield a "daughter" by inserting one nitrogen atom into the m-OPE core. We find that if the substituted nitrogen is in a meta position relative to both acetylene linkers, the daughter conductance remains as low as the parent. However, if the substituted nitrogen is in an ortho position relative to one acetylene linker and a para position relative to the other, destructive QI is alleviated and the daughter conductance is high. This behavior contrasts with that of a para-connected parent, whose conductance is unaffected...
Constructive Quantum Interference in Single‐Molecule Benzodichalcogenophene Junctions
Chemistry – A European Journal, 2020
Heteroatom substitution into the cores of alternant, aromatic hydrocarbons containing only even-membered rings is attracting increasing interest as a method of tuning their electrical conductance. Here we examine the effect of heteroatom substitution into molecular cores of non-alternant hydrocarbons, containing oddmembered rings. Benzodichalcogenophene (BDC) compounds are rigid, planar π-conjugated structures, with molecular cores containing 5-membered rings fused to a 6-membered aryl ring. To probe the sensitivity or resilience of constructive quantum interference (CQI) in these non-bipartite molecular cores, two C 2-symmetric molecules (I and II) and one asymmetric molecule (III) are investigated. I (II) contains S (O) heteroatoms in each of the 5-membered rings, while III contains an S in one 5-membered ring and an O in the other. Differences in their conductances arise primarily from the longer S-C and shorter O-C bond lengths compared with the CC bond and the associated changes in their resonance integrals. We find that although the conductance of III is significantly lower than the conductances of the others, CQI is resilient and persists in all molecules.
Modulation and Control of Charge Transport Through Single-Molecule Junctions
Topics in current chemistry (Journal), 2017
The ability to modulate and control charge transport though single-molecule junction devices is crucial to achieving the ultimate goal of molecular electronics: constructing real-world-applicable electronic components from single molecules. This review aims to highlight the progress made in single-molecule electronics, emphasizing the development of molecular junction electronics in recent years. Among many techniques that attempt to wire a molecule to metallic electrodes, the single-molecule break junction (SMBJ) technique is one of the most reliable and tunable experimental platforms for achieving metal-molecule-metal configurations. It also provides great freedom to tune charge transport through the junction. Soon after the SMBJ technique was introduced, it was extensively used to measure the conductances of individual molecules; however, different conductances were obtained for the same molecule, and it proved difficult to interpret this wide distribution of experimental data. T...
Dependence of single-molecule junction conductance on molecular conformation
Nature, 2006
The conductance of a single metal-molecule-metal junction depends not only on the chemical nature of the molecule used, but also on its conformation 1-4 . In the simple case of a biphenyl-two phenyl rings linked by a single C-C bond-conductance is expected to change with the relative twist angle between the two rings, with the planar conformation having the highest conductance. A number of different techniques have measured the conductance of metal-molecule(s)-metal junctions 5-12 .
Electrochemistry Communications, 2016
In this work, the conductance of molecules with different alkyl length between benzene and carboxylic acid at each side are explored by electrochemical jump-to-contact STM break junction. The results show that the quantum interference (QI) is found in meta-phenylenedipropionic acid containing two methylene groups between benzene ring and carboxylic acid, and there is no obvious QI effect for meta-phthalic acid and meta-phenylenediacetic acid with shorter alkyl between benzene and carboxylic acid. We attribute the disappearance of the QI in meta-phthalic acid and meta-phenylenediacetic acid to the strong interaction between the benzene ring and anchoring group when they are too close. The current result reveals the importance role of alkyl chain on benzene ring and anchoring group in QI effect.