Toward Multiple Conductance Pathways with Heterocycle-Based Oligo(phenyleneethynylene) Derivatives

Abstract

In this paper, we have systematically studied how the replacement of a benzene ring by a heterocyclic compound in oligo(phenyleneethynylene) (OPE) derivatives affects the conductance of a molecular wire using the scanning tunneling microscope-based break junction technique. We describe for the first time how OPE derivatives with a central pyrimidine ring can efficiently link to the gold electrode by two pathways presenting two different conductance G values. We have demonstrated that this effect is associated with the presence of two efficient conductive pathways of different length: the conventional end-to-end configuration, and another with one of the electrodes linked directly to the central ring. This represents one of the few examples in which two defined conductive states can be set up in a single molecule without the aid of an external stimulus. Moreover, we have observed that the conductance through the full length of the heterocycle-based OPEs is basically unaffected by the presence of the heterocycle. All these results and the simplicity of the proposed molecules push forward the development of compounds with multiple conductance pathways, which would be a breakthrough in the field of molecular electronics.

Gating of Quantum Interference in Molecular Junctions by Heteroatom Substitution

“…As depicted in Figure 1 C, the presence of the nitrogen atom shows no distinguishable effect on the constructive QI in the junctions through the para ‐coupled molecules p ‐OPE and P , which is in good agreement with Ref. 7c and the results obtained by Gonzalez et al 7b…”

“…Interestingly, there is no significant conductance feature of the molecular junctions with one of Au electrodes connected directly to the central pyridine ring via the Au−N bonds, as observed in the analogous system containing a pyrimidine ring 7b. This observation can be attributed to the significant binding force difference between the Au−S covalent bond (1.2 nN)10 and the Au−N bond (0.8 nN)11 that is close to the Au−S (methylsulfide) bond (0.7 nN),12 leading to a preference for the covalent Au−S over the Au−N binding motif in the present case.…”

Conductance in a bis-terpyridine based single molecular breadboard circuit

“…17,18,38 Experimental observables include conductance values and the most probable electrode separations at which they occur (Fig. 3C).…”

“…By substituting the central benzene ring with sulfur and nitrogen heterocycles, the authors were able to demonstrate a new high conductance channel formed by the linking of the central pyrimidine ring to the electrodes. 18 More recently, Kiguchi and co-workers have also shown the existence of 3 conductance states within a tripyridyl–triazine molecular junctions. 38 In the studies above 17,18,38 single circuits were assigned to each conductance state observed in the experiments and upto 3 circuits across the molecular scaffold were proposed to be accessible by the experiments.…”

“…4–8 In STM-BJ/MCBJ, single molecules are contacted by two electrodes to form a metal–molecule–metal junction. Under the application of a bias voltage, the current flowing through the molecule, from one electrode to the other is sensitive to the molecular structure (length, conjugation pattern and conformation), 9,10 the chemical nature of the linker which connects the molecule to the electrode, 6,11–13 the relative position of linkers attached to the molecular core, 14,15 the binding geometry of molecule between the electrodes, 16–18 and the effect of external triggers on molecular structure and environment. 2,6,19–22 Thus, these experimental techniques when combined with charge transport theory present a unique opportunity to create dynamic circuits with a library of molecules, which can act like wires, 9,23–25 switches 26,27 and diodes.…”