Multiple-channel and symmetry-breaking effects on molecular conductance via side substituents

Chemical substitution represents a pivotal method that enables effective modulation of molecular conductance and production of multiple transport channels, quantum interference effects, and other mechanisms. However, the intricate interplay that occurs between the molecular backbone and the side motifs remains largely unexplored. This study explores the conductance characteristics of molecular junctions that feature different σ and π side groups by using a synergistic approach that combines scanning tunneling microscope break junction experiments with the results of first-principles calculations. Our analysis shows that the incorporation of σ-side groups induces symmetry breaking in the frontier orbitals and increases intramolecular scattering, which then leads to reduced conductance. Conversely, the integration of π-side groups augments the molecular conductance through the multiple-channel effect, by which an additional π pathway is introduced for charge transport. The findings reported here provide valuable insights into both molecular functionalization and the future design of potential molecular electronic devices.