Substituent-mediated quantum interference toward a giant single-molecule conductance variation

Abstract

Quantum interference (QI) in single molecular junctions shows a promising perspective for realizing conceptual nanoelectronics. However, controlling and modulating the QI remains a big challenge. Herein, two-type substituents at different positions of meta-linked benzene, namely electron-donating methoxy (–OMe) and electron-withdrawing nitryl (–NO2), are designed and synthesized to investigate the substituent effects on QI. The calculated transmission coefficients T(E) indicates that –OMe and –NO2 could remove the antiresonance and destructive quantum interference (DQI)-induced transmission dips at position 2. –OMe could raise the antiresonance energy at position 4 while –NO2 groups removes the DQI features. For substituents at position 5, both of them are nonactive for tuning QI. The conductance measurements by scanning tunneling microscopy break junction show a good agreement with the theoretical prediction. More than two order of magnitude single-molecule conductance on/off ratio could be achieved at the different positions of –NO2 substituent groups at room temperature. The present work proves chemical substituents can be used for tuning QI features in single molecular junctions, which provides a feasible way toward realization of high-performance molecular devices.