Additive Electron Pathway and Nonadditive Molecular Conductance by Using a Multipodal Bridging Compound

We designed and synthesized a new quadrivial anchoring unit 4-TEB, to construct a stable single-molecule junction with gold electrodes, which should have equivalent conducting electron pathways between two electrodes. The conductances of single-molecule junctions comprising 4-TEB and its bidirectional counterpart 2-TEB were determined to be 2.7 × 10^–4G₀ (2e²/h) and 5.0 × 10^–5G₀, respectively, by using scanning tunneling microscope break junction (STM-BJ) techniques. The single 4-TEB molecule junction had higher stability and conductivity compared to those of the single 2-TEB molecule junction. Although the number of electron pathways from/to the electrode to/from the molecule was additive using the equivalent multianchoring, the conductance of the single-molecule junction was not additive. From first-principles electronic transport calculations, the mechanism for the new quadrivial 4-TEB single-molecule junction involved an overlap resonance effect to the HOMO conducting orbital, giving rise to tunneling. Using fixed nanogap electrodes, we constructed stable molecular junctions of 4-TEB and observed symmetric peaks in the derivative of the conductance–voltage (G–V) curves, which were assigned to electron transport through the HOMO on the basis of theoretical calculations.