Conjugation-regulated lateral and stereoelectronic effects in single-molecule junctions

Conjugated molecules have diverse applications across electronics, optoelectronics, and sensors. Their conjugated characteristics determine the molecular electronic and photonic properties, which are crucial for the design of functional materials. This study investigates the conjugation-regulated molecular transport properties by a combination of scanning tunneling microscopy break junction technologies and theoretical simulations. Two conductance states, which originate from it-contact and a-contact, respectively, are found and can be further regulated by conjugation. With increasing conjugation, the high conductance state of it-contact can be enhanced through the lateral effect between the molecular conjugated backbones and gold substrates, while the low conductance state of a-contact, which varies with the molecular torsion angle, is mainly affected through the stereoelectronic effect. Moreover, the high electric field increases the lateral interaction of the it-contacts while decreasing the conductance of the a-contacts. These conjugation-regulated lateral and stereoelectronic effects provide valuable insights into functionalization and optimization of molecular materials and devices.