Exceptional Single-Molecule Transport Properties of Ladder-Type Heteroacene Molecular Wires

Abstract

A series of ladder-type fused heteroacenes consisting of thiophenes and benzothiophenes were synthesized and functionalized with thiol groups for single-molecule electrical measurements via a scanning tunneling microscopy break-junction method. It was found that this molecular wire system possesses exceptional charge transport properties with weak length dependence. The tunneling decay constant β was estimated to be 0.088 and 0.047 Å(-1) under 0.1 and 0.5 bias, respectively, which is one of the lowest β values among other non-metal-containing molecular wires, indicating that a planar ladder structure favors charge transport. Transition voltage spectroscopy showed that the energy barrier decreases as the length of the molecule increases. The general trend of the energy offsets derived from the transition voltage via the Newns-Anderson model agrees well with that of the Fermi/HOMO energy level difference. Nonequilibrium Green's function/density functional theory was used to further investigate the transport process in these molecular wires.

Hemilabile Ligands as Mechanosensitive Electrode Contacts for Molecular Electronics

“…In addition to expanding the molecular‐electronics toolbox with new design ideas for molecular termini and contacts, our results shed light on the mechanism of configuration transitions in thienyl‐based hemilabile ligands, showing that the fabrication of single‐molecule junctions doubles also as a valuable characterisation tool to probe metal–ligand interactions. Furthermore, (methylthio)thiophenes and thiophenethiols are widely used as molecular‐wire termini in molecular electronics, and our results unambiguously demonstrate that contact‐configuration changes must be taken into account when interpreting their conductance‐vs.‐electrode‐separation trajectories during a single‐entity break‐junction experiment.…”

Molecular Design towards Controlling Charge Transport

“…The second strategy involves the lowering of HOMO–LUMO gap by coupling of donor and acceptor moieties through π‐conjugated bridges . Employing the first strategy, Yu's group recently demonstrated the efficacy of locked ladder systems towards enhancing charge transport in molecular wires . Building upon their previous work, his group synthesized a series of ladder‐type thienoacene‐based molecular wires with 3, 5, 7, 9, and 11 rings in their backbone; these were further functionalized with thiol groups for direct assembly onto a gold surface (Figure ) .…”

“… a) Transmission spectra of molecular junctions at low bias. b) Theoretical and experimental I – V curves (Copyright 2016, American Chemical Society) …”

“…Detailed conductance measurements revealed two conductance plateaus in the decay curves for MW‐S and MW‐Se, but only one conductance plateau in the decay curve for MW‐N. The high‐conductance plateaus for MW‐S and MW‐Se are around 10 −3 G 0 , while their low‐conductance plateaus are around 10 −4 G 0 , which is close to the conductance plateau observed for MW‐N and fused HA9 molecular wire described above . The high‐conductance plateau was assigned to the charge‐transport pathway between a thiol anchoring group and the central benzodiazole acceptor ring, while the low‐conductance plateau corresponds to the conducting pathway between the thiol anchoring groups.…”

Spin Logic Gates Operated by Protonation and Magnetism in Molecular Combinational Circuits

“…[1] Simple molecular electronic functional devices, such as molecular rectifiers, [2,3] molecular switches, [4,5] molecular wires [6,7] and molecular sensors [8][9][10] have been designed theoretically and synthesized experimentally on single-molecular scale. [1] Simple molecular electronic functional devices, such as molecular rectifiers, [2,3] molecular switches, [4,5] molecular wires [6,7] and molecular sensors [8][9][10] have been designed theoretically and synthesized experimentally on single-molecular scale.…”