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

We designed and synthesized a new quadrivial anchoring unit <b>4-TEB</b>, 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 <b>4-TEB</b> and its bidirectional counterpart <b>2-TEB</b> were determined to be 2.7 × 10<sup>–4</sup><i>G</i><sub>0</sub> (2<i>e</i><sup>2</sup>/<i>h</i>) and 5.0 × 10<sup>–5</sup><i>G</i><sub>0</sub>, respectively, by using scanning tunneling microscope break junction (STM-BJ) techniques. The single <b>4-TEB</b> molecule junction had higher stability and conductivity compared to those of the single <b>2-TEB</b> 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 <b>4-TEB</b> 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 <b>4-TEB</b> and observed symmetric peaks in the derivative of the conductance–voltage (<i>G–V</i>) curves, which were assigned to electron transport through the HOMO on the basis of theoretical calculations.