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

Abstract

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.

Highly-conducting molecular circuits based on antiaromaticity

“…The observed behaviour with the quasi-sigmoidal shape of the conductance modulation is similar to one of two distinct profiles recurrently found in the literature for both organic and organometallic derivatives in aqueous electrolytes383940. A sigmoidal shape of the molecular conductance modulation has been observed previously in studies of electrochemically gated conductance of viologen-based single-molecule junctions in aqueous electrolytes and attributed to a ‘soft’ electrochemical gating of the conductance response4041.…”

Enhanced Separation Concept (ESC): Removing the Functional Subunit from the Electrode by Molecular Design

“…Numerous systems have been reported being addressed by various stimuli like e.g. light,, mechanical manipulation,, electrochemical gating,, the applied voltage, or the electrical current , . We became recently interested in E ‐field triggered molecular junctions and developed a variety of model compounds sensing this parameter.…”

Quantum interference in coherent tunneling through branched molecular junctions containing ferrocene centers

“…24 lies in bringing all these structural aspects together in a single molecule, which could allow in principle to combine redox-gated fluctuations of the electron population at ferrocene moieties as a switching mechanism between two redox states, where DQI effects would guarantee a very low conductance for one of them and their absence a significantly higher conductance for the other one. A similar idea for a redox-gated switch, where one state of the redox pair was designed to exhibit DQI effects, has recently been pursued with anthraquinone derivatives but the ON/OFF ratios were found to be rather modest, since DQI occurred rather far in energy from the Fermi level (E F ) in the transmission function 36 . Although the synthesis part of Ref.…”