Distinguishing quantum interference in metaconnected molecular systems

Metaconnected benzene shows destructive quantum interference in charge transport. Whether metaconnection always indicates destructive quantum interference is not yet well understood. Herein, we compare two meta structures, meta-terminated paraterphenyl (meta1) and metaterphenyl (meta2), through tight-binding modeling of simplified structures, as well as synthesis, single-molecule conductance measurements, and self-energy corrected density-functional theory calculations of three series of molecules. Meta2 exhibits a much stronger quantum interference effect than meta1 in single-molecule junction charge transport. When the second-nearest neighbor interaction between the molecule and the electrodes $({\mathrm{\ensuremath{\Gamma}}}_{1})$ is included, the tight-binding model successfully captures the difference between meta1 and meta2. Through tight-binding modeling of benzene, biphenyl, and tetraphenyl structures, we suggest that when ${\mathrm{\ensuremath{\Gamma}}}_{1}$ enables coupling between para or ortho positions on the terminal benzene to the electrode, overall destructive quantum interference is suppressed; when ${\mathrm{\ensuremath{\Gamma}}}_{1}$ continues to be a coupling between meta positions to the electrode, destructive quantum interference remains. Our findings highlight that different degrees of destructive quantum interference effect can be readily achieved through the design of varied metaconnected molecular structures.