Asymmetric Electronic Transport in Porphine: Role of Atomically Precise Tip Electrode

Abstract

Electronic conductance through a single molecule is sensitive to its structural orientation between two electrodes, owing to the distribution of molecular orbitals and their coupling to the electrode levels, that are governed by quantum confinement effects. Herein, the contact geometry of the porphine molecule is varied by attaching two Au tip electrodes that resemble the mechanical break junction, via thiol anchoring groups, is varied. The current–voltage characteristics of all the contact geometries are investigated using nonequilibrium Green's function formalism along with density functional theory and tight‐binding framework. Varying current responses are observed with changing contact sites, originating from varied wave‐function delocalization and quantum interference effect. The calculations show asymmetric current–voltage characteristics under forward and reverse biases due to structural asymmetry of the tip electrodes on either side of the molecule. This phenomenon is established as a universal feature for any molecular electronic device, irrespective of the inherent structural symmetry of a molecule. These findings provide fundamental insights into electronic transport through single molecules in the real experimental setup. Furthermore, the observations of varying current response can further motivate the fabrication of sensor devices with porphine‐based biomolecules that control important physiological activities, in view of their applications in advanced diagnostics.