Molecular Structure-(Thermo)electric Property Relationships in Single-Molecule Junctions and Comparisons with Single- and Multiple-Parameter Models

The most probable single-molecule conductance of each member of a series of 12 conjugated molecular wires, 6 of which contain either a ruthenium or platinum center centrally placed within the backbone, has been determined. The measurement of a small, positive Seebeck coefficient has established that transmission through these molecules takes place by tunneling through the tail of the HOMO resonance near the middle of the HOMO-LUMO gap in each case. Despite the general similarities in the molecular lengths and frontier-orbital compositions, experimental and computationally determined trends in molecular conductance values across this series cannot be satisfactorily explained in terms of commonly discussed single-parameter models of junction conductance. Rather, the trends in molecular conductance are better rationalized from consideration of the complete molecular junction, with conductance values well described by transport calculations carried out at the DFT level of theory, on the basis of the Landauer-Buttiker model.

Automated summary

The conductance of a series of 12 conjugated molecular wires, including 6 with ruthenium or platinum center, has been determined. The transmission through these wires is mainly through tunneling at the tail of the HOMO resonance near the middle of the HOMO-LUMO gap. The trends in molecular conductance across the series cannot be explained solely by single-parameter models, but require consideration of the complete molecular junction.