Two-dimensional assembly and local redox-activity of molecular hybrid structures in an electrochemical environment

Li, Zhihai; Han, Bo; Mészáros, Gábor; Pobelov, Ilya V.; Wandlowski, Thomas; Błaszczyk, Alfred; Mayor, Marcel

doi:10.1039/b506623a

Cited by 142 publications

(259 citation statements)

References 106 publications

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“…In the electrochemical scanning tunneling spectroscopy configuration (i.e., STM tip not chemically attached to the molecule) there is now a collection of examples displaying a clear maximum in their tunneling current (I tunneling ) vs electrochemical potential relations. 13,15,[23][24][25][26][27]29,39 These have been well-modeled in terms of the KU relationship for two-step electron/hole transfer through the redox center in the STM−substrate gap. The situation is far from clear for measurements made in the in situ electrochemically gated BJ configuration (i.e., when the electrochemically active bridge molecule is chemically attached at one end to the STM tip and at the other end to the substrate).…”

Section: ■ Introductionmentioning

confidence: 99%

Single-Molecule Electrochemical Gating in Ionic Liquids

et al. 2012

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The single-molecular conductance of a redox active molecular bridge has been studied in an electrochemical single-molecule transistor configuration in a room-temperature ionic liquid (RTIL). The redox active pyrrolo-tetrathiafulvalene (pTTF) moiety was attached to gold contacts at both ends through −(CH2)6S– groups, and gating of the redox state was achieved with the electrochemical potential. The water-free, room-temperature, ionic liquid environment enabled both the monocationic and the previously inaccessible dicationic redox states of the pTTF moiety to be studied in the in situ scanning tunneling microscopy (STM) molecular break junction configuration. As the electrode potential is swept to positive potentials through both redox transitions, an ideal switching behavior is observed in which the conductance increases and then decreases as the first redox wave is passed, and then increases and decreases again as the second redox process is passed. This is described as an “off–on–off–on–off” conductance switching behavior. This molecular conductance vs electrochemical potential relation could be modeled well as a sequential two-step charge transfer process with full or partial vibrational relaxation. Using this view, reorganization energies of ∼1.2 eV have been estimated for both the first and second redox transitions for the pTTF bridge in the 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIOTf) ionic liquid environment. By contrast, in aqueous environments, a much smaller reorganization energy of ∼0.4 eV has been obtained for the same molecular bridge. These differences are attributed to the large, outer-sphere reorganization energy for charge transfer across the molecular junction in the RTIL.

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Section: ■ Introductionmentioning

confidence: 99%

Single-Molecule Electrochemical Gating in Ionic Liquids

et al. 2012

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“…Conductance switching in molecular junctions has been demonstrated previously using various means including light, 1, 2 bias pulses, 3 electrostatic-, 4,5 and electrochemical gating. 6,7 The concept of "electrochemical gating" which provides the opportunity to overcome the technical challenges of incorporating a gate electrode in a solid-state molecular device, has been employed in electrochemically active molecular systems, including viologens, [8][9][10] oligoaniline, 11 ferrocene, [12][13][14] transition metal complexes, 7,15,16 perylenebisimides, [17][18][19] redox-active proteins, 20,21 quinones 22,23 and tetrathiafulvalene, 24 as well as redox-inactive molecules. 25 In the case of redox-inactive molecules, or more generally when the electrode potential does not overlap with the molecule's redox potential, the effect of the gate is simply to shift the molecular levels up or down in energy relative to the Fermi level.…”

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confidence: 99%

Electrochemical Control of Single-Molecule Conductance by Fermi-Level Tuning and Conjugation Switching

et al. 2014

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Controlling charge transport through a single molecule connected to metallic electrodes remains one of the most fundamental challenges of nanoelectronics. Here we use electrochemical gating to reversibly tune the conductance of two different organic molecules, both containing anthraquinone (AQ) centers, over >1 order of magnitude. For electrode potentials outside the redox-active region, the effect of the gate is simply to shift the molecular energy levels relative to the metal Fermi level. At the redox potential, the conductance changes abruptly as the AQ unit is oxidized/reduced with an accompanying change in the conjugation pattern between linear and cross conjugation. The most significant change in conductance is observed when the electron pathway connecting the two electrodes is via the AQ unit. This is consistent with the expected occurrence of destructive quantum interference in that case. The experimental results are supported by an excellent agreement with ab initio transport calculations.

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“…20 This expectation has been supported by a number of recent experimental studies. [31][32][33][34][35][36][37][38] Not only the maximum itself has been clearly observed but the dependence of maximum current and the position of the maximum on the bias voltage has also been studied 32,33 and analyzed. 32 Closer examination of Tao's data shows that the current maximum for this system is also close to the equilibrium potential.…”

Section: Introductionmentioning

confidence: 99%

Electric double layer effect on observable characteristics of the tunnel current through a bridged electrochemical contact

Кузнецов

Medvedev

Ulstrup

2007

The Journal of Chemical Physics

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Scanning tunneling microscopy and electrical conductivity of redox molecules in conducting media (aqueous or other media) acquire increasing importance both as novel single-molecule science and with a view on molecular scale functional elements. Such configurations require full and independent electrochemical potential control of both electrodes involved. We provide here a general formalism for the electric current through a redox group in an electrochemical tunnel contact. The formalism applies broadly in the limits of both weak and strong coupling of the redox group with the enclosing metal electrodes. Simple approximate expressions better suited for experimental data analysis are also derived. Particular attention is given to the effects of the Debye screening of the electric potential in the narrow tunneling gap based on the limit of the linearized Poisson-Boltzmann equation. The current/overpotential relation shows a maximum at a position which depends on the ionic strength. It is shown, in particular, that the dependence of the maximum position on the bias voltage may be nonmonotonous. Approximate expressions for the limiting value of the slope of the current/overpotential dependence and the width of the maximum on the bias voltage are also given and found to depend strongly on both the Debye screening and the position of the redox group in the tunnel gap, with diagnostic value in experimental data analysis.

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Two-dimensional assembly and local redox-activity of molecular hybrid structures in an electrochemical environment

Cited by 142 publications

References 106 publications

Single-Molecule Electrochemical Gating in Ionic Liquids

Single-Molecule Electrochemical Gating in Ionic Liquids

Electrochemical Control of Single-Molecule Conductance by Fermi-Level Tuning and Conjugation Switching

Electric double layer effect on observable characteristics of the tunnel current through a bridged electrochemical contact

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