Conformation dependence of molecular conductance: chemistry versus geometry

Finch, Christopher; Sirichantaropass, Skon; Bailey, Steven W.; Grace, Iain; García‐Suárez, Víctor M.; Lambert, Colin J.

doi:10.1088/0953-8984/20/02/022203

Cited by 50 publications

(58 citation statements)

References 23 publications

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“…3,16,17 In this regard, calculations based on the approximate density functional theory (DFT) can be helpful to obtain a better understanding of the charge transport mechanisms involved and to interpret trends in the experimental data based on computed structuretransport relationships. In agreement with the experimental observations, they show, in particular, that the electric conduction strongly depends on the molecular conformation [4][5][6][18][19][20][21][22][23] and the precise geometry in the single-molecule junctions.…”

Section: Introductionsupporting

confidence: 87%

Conduction mechanisms in biphenyl dithiol single-molecule junctions

et al. 2012

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Based on density-functional theory calculations, we report a detailed study of the single-molecule charge-transport properties for a series of recently synthesized biphenyl-dithiol molecules [D. Vonlanthen et al., Angew. Chem., Int. Ed. 48, 8886 (2009); A. Mishchenko et al., Nano Lett. 10, 156 (2010)]. The torsion angle ϕ between the two phenyl rings, and hence the degree of π conjugation, is controlled by alkyl chains and methyl side groups. We consider three different coordination geometries, namely top-top, bridge-bridge, and hollow-hollow with the terminal sulfur atoms bound to one, two, and three gold surface atoms, respectively. Our calculations show that different coordination geometries give rise to conductances which vary by one order of magnitude for the same molecule. Irrespective of the coordination geometries, the charge transport calculations predict a cos 2 ϕ dependence of the conductance, which is confirmed by our experimental measurements. We demonstrate that the calculated transmission through biphenyl dithiols is typically dominated by a single transmission eigenchannel formed from π electrons. For perpendicular orientation of the rings a residual conductance arises from σ-π couplings. But only for a single molecule with a completely broken conjugation we find a nearly perfect degeneracy of the σ-π eigenchannels for the hollow-hollow-type contact in our theory.

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Section: Introductionsupporting

confidence: 87%

Conduction mechanisms in biphenyl dithiol single-molecule junctions

et al. 2012

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“…As the phenyl rings are rotated from 0°t o 60°in BPDT, the conjugation of the molecular backbone is reduced, which moves the LUMO level up in energy and reduces the transmission at the Fermi energy, following a known cos 2 ͑͒ law. [31][32][33] However the overall shape of the transmission remains almost unchanged. In contrast the CSW-479 molecule possesses a Fano resonance near the Fermi energy and as the side group is rotated, the Fano resonance moves to a lower energy, leading to a significant change in the slope of T͑E͒ near E = E F .…”

Section: ͑1͒mentioning

confidence: 99%

“…In what follows we examine the effect of rotating either the phenyl rings in BPDT or the side group in CSW-479, which could be induced by tilting the molecule using an STM tip 3 or via steric hindrance. [30][31][32][33] The sections of the molecules to rotate are chosen so that in BPDT the coupling along the backbone and in CSW-479 the coupling to the side group ͑see Fig. 1͒ is changed.…”

Section: ͑1͒mentioning

confidence: 99%

Giant thermopower and figure of merit in single-molecule devices

2009

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We present a study of the thermopower S and the dimensionless figure of merit ZT in molecules sandwiched between gold electrodes. We show that for molecules with side groups, the shape of the transmission coefficient can be dramatically modified by Fano resonances near the Fermi energy, which can be tuned to produce huge increases in S and ZT. This shows that molecules exhibiting Fano resonances have a high efficiency of thermoelectric cooling which is not present for conventional ungated molecules with only delocalized states along their backbone. Single-molecule devices offer a potential route to sub-10-nm electronics. For the purpose of designing large-scale integration of such devices, knowledge of thermal as well as electrical properties is needed. Furthermore, knowledge of thermoelectric properties of single molecules 10 may underpin novel thermal devices such as molecular-scale Peltier coolers and provide new insight into mechanisms for molecular-scale transport. For example, from the sign of the thermopower it is possible to deduce the conduction mechanism or relative position of the Fermi energy, 11 with a positive sign indicating p-type conduction, which means the Fermi energy is lying closer to the highest occupied molecular orbital ͑HOMO͒ level. The thermopower can also exhibit very interesting behaviors, such as a linear increase with the molecular length.12 Other theoretical studies have shown the possibility of changing both the sign and magnitude of the thermopower by electrically gating a molecular wire, 13,14 which moves the Fermi energy across a transmission resonance and thus changes its sign.However when the Fermi energy lies within the HOMOlowest unoccupied molecular orbital ͑LUMO͒ gap, thermopower is expected to be low. Indeed recently, Reddy et al.15 measured the room-temperature thermopower of 1,4-biphenyldithiol ͑BPDT͒, using a modified scanning tunnel microscope. They found the thermopower to be +12.9 V K −1 . This low value was attributed to the Fermi energy sitting within the molecule's HOMO-LUMO gap where both the density of states ͑DOS͒ and transmission coefficients are relatively flat.In this Brief Report we show that much higher values can be obtained from molecules exhibiting Fano resonances. We investigate the thermoelectric properties of two different molecules, the BPDT and CSW-470-bipyridine ͑CSW-479͒, 16 as a function of the rotation angles of some of the molecular groups. Both exhibit Breit-Wigner-type resonances in the transmission coefficient T͑E͒ near the Fermi level corresponding to the HOMO and LUMO levels. However, CSW-479 also possesses states associated with the bipyridine side group, which are weakly coupled to the backbone and produce an additional Fano resonance in the electron transmission coefficients. 17,18 The position of the In what follows, we demonstrate that changing the conformation of the side group in CSW-479 moves the Fano resonance close to the Fermi energy and creates huge changes in the magnitudes of the thermopower and can even change its sign, w...

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“…They are attractive from a single-molecule perspective because they are rigid structures and avoid complexities associated with ring rotations. 13,14 Furthermore, in contrast with graphene ribbons, whose edges suffer from atomic-scale uncertainties and are therefore expected to exhibit Levy flights 23 rather than ballistic transport, these families of molecules have well-defined edges and therefore electron transport is potentially ballistic.…”

mentioning

confidence: 99%

“…46 Nevertheless, systematic trends in families of molecules have been predicted and compared favorably with experiment. [13][14][15][16][17][18][19] In this paper, we have calculated the roomtemperature, low-bias conductance of three ribbonlike families of molecules. The conductance of the fluorenes and phenanthrenes decays exponentially with length, whereas the conductance of the acene series is an oscillatory function of the length.…”

mentioning

confidence: 99%

Electron transport through ribbonlike molecular wires calculated using density-functional theory and Green’s function formalism

2010

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We study the length dependence of electron transport through three families of rigid, ribbonlike molecular wires. These series of molecules, known as polyacene dithiolates, polyphenanthrene dithiolates, and polyfluorene dithiolates, represent the ultimate graphene nanoribbons. We find that acenes are the most attractive candidates for low-resistance molecular-scale wires because the low-bias conductance of the fluorene-and phenanthrene-based families is shown to decrease exponentially with length, with inverse decay lengths of ␤ = 0.29 Å −1 and ␤ = 0.37 Å −1 , respectively. In contrast, the conductance of the acene-based series is found to oscillate with length due to quantum interference. The period of oscillation is determined by the Fermi wave vector of an infinite acene chain and is approximately 10 Å. Details of the oscillations are sensitive to the position of thiol end groups and in the case of "para" end groups, the conductance is found initially to increase with length.

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Conformation dependence of molecular conductance: chemistry versus geometry

Cited by 50 publications

References 23 publications

Conduction mechanisms in biphenyl dithiol single-molecule junctions

Conduction mechanisms in biphenyl dithiol single-molecule junctions

Giant thermopower and figure of merit in single-molecule devices

Electron transport through ribbonlike molecular wires calculated using density-functional theory and Green’s function formalism

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