Freezing the conductance of platinum(II) complexes by quantum interference effect

Understanding the impact of substituents on the quantum interference effect at single molecule scale is of great importance for the design of molecular devices. In this work, three platinum(II) complexes with -H, -NH2 and -NO2 groups on conductive backbones were designed and synthesized. Single-molecule conductance, which was measured using scanning tunnelling microscope break junction (STM-BJ) technique, demonstrated a conductance freeze phenomenon under the variation of substituents. Theoretical study revealed that, despite the electronic effect of the substituents shifting the energy level of molecular orbital, the quantum interference effect vanished the influence of electronic effect on the conductance and eventually leaded to the conductance freeze.