Experimental Validation of Quantum Circuit Rules in Molecular Junctions

Abstract

A series of diarylacetylene (tolane) derivatives functionalised at the 4-and 4 0 -positions by thiolate, thioether, or amine groups capable of serving as anchor groups to secure the molecules within a molecular junction have been prepared and characterised. The series of compounds have a general form X-B-X, Y-B-Y, and X-B-Y where X and Y represent anchor groups and B the molecular bridge. The single-molecule conductance values determined by the scanning tunnelling microscope break-junction method are found to be in excellent agreement with the predictions made on the basis of a recently proposed 'molecular circuit law', which states 'the conductance G XBY of an asymmetric molecule X-B-Y is the geometric mean ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi G XBX G YBY p of the conductance of the two symmetric molecules derived from it, G XBX and G YBY .' The experimental verification of the circuit law, which holds for systems in which the constituent moieties X, B, and Y are weakly coupled and whose conductance takes place via off-resonance tunnelling, gives further confidence in the use of this relationship in the design of future compounds for use in molecular electronics research.

Planar aromatic anchors control the electrical conductance of gold|molecule|graphene junctions

“…Molecular junctions, in which one or more molecules bridge the gap between a source and drain electrode, have been intensely studied during the past two decades. 1–17 A variety of methods for engineering the transport properties of molecules have been developed, based on manipulating conformation, 18–22 anchor groups, 8,23–27 electrodes, 28–31 quantum interference, 32–42 and heteroatom substitution, 43–48 both in single-molecule junctions and large-area junctions comprising self-assembled monolayers (SAMs) of organic molecules. 29,49–51 Typically in single-molecule experiments using mechanically controllable break junction (MCBJ) 1 or scanning tunnelling microscope (STM) 2 contacting methodologies, gold is the electrode material of choice.…”

A one-pot synthesis of oligo(arylene–ethynylene)-molecular wires and their use in the further verification of molecular circuit laws

“…From these experimental data, the relevant anchor group parameters, a X (Table 1), and the circuit rule (Eqn 3) it is possible to calculate, test and refine backbone parameters, b B , for the 2,5-diethynylthiophene (b thioph ), 1,4-diethynylnaphthalene (b naphth ) and 9,10-diethynylanthracene (b anth ) fragments. In the first instance, given the anchor parameters for the thioanisole (a SMe = −1.41) and DMBT (a DMBT = −1.21) moieties, [19] and the experimentally determined molecular conductance of the 2,5-diethynylthiophene compounds 5b (log(G/G 0 ) = −3.81 ± 0.36) and 5c (log(G/G 0 ) = −3.77 ± 0.36) (Table 3) it is possible to estimate the bridge parameter b thioph (−1.17) from the average solutions of Eqn 3. Alternatively, averaging the values of b thioph obtained from each of the three experimental conductance values from 5a, 5b and 5c gives b thioph = −1.18, a value obviously similar to the two-point estimate given above.…”

“…[18] A number of these parameters have been determined from both computational and experimental conductance data, providing the basis of a 'tool kit' for exploring molecular structure-electrical property relationships and molecular design strategies (Table 1, 2). [18,19] However, before the potential of the circuit laws can be fully realised, more such parameters need to be determined from conductance data of systematically varied molecular structures.…”

“…G/G 0 )) to Eqn 3. [ 18,19] www.publish.csiro.au/ch Australian Journal of Chemistry gold electrodes are readily identified as initial targets. For gold-electrode based molecular junctions, thiol-based anchor groups are frequently used in both single molecules and large area junctions due to the strong gold-sulfur bond, the often high junction formation probability and the propensity of thiols (as thiolates) to form well-packed self-assembled monolayers (SAMs) with a high stability on gold.…”

Celebrating RACI and Academy of Science Awards 2020–2021

“…The single-molecule conductance values determined by the scanning tunnelling microscope break-junction method were found to be in excellent agreement with the predictions made on the basis of this law. [7] Thomas Maschmeyer (The University of Sydney) was the 2021 recipient of the David Craig Medal of the AAS. He contributes a paper with J. Strachan, L. Chen, T. Ellis, and A.…”