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 (Γ1) 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 Γ1 enables coupling between para or ortho positions on the terminal benzene to the electrode, overall destructive quantum interference is suppressed; when Γ1 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.

Read more at Physical Review B:
https://journals.aps.org/prb/abstract/10.1103/tjrz-czl7

Photo caption:
(a) Tight-binding model and (b) corresponding transmissions for para, meta1, and meta2. 𝑡=1 and Γ𝐿=Γ𝑅=0.1. (c) Refined tight-binding model and (d) corresponding transmissions for para, meta1, and meta2. The coupling strength of the bonds connecting neighboring phenyls is represented by 𝑡1 (pink). Two types of second-nearest neighbor interactions are represented by 𝑡2 (within a phenyl, orange) and 𝑡3 (between phenyls, blue), respectively. The second-nearest neighbor interaction between the molecule and the electrode is represented by Γ1 (gray). 𝑡=1, Γ𝐿=Γ𝑅=0.1, 𝑡1=cos⁡37∘×𝑡=0.77, 𝑡2=0.33, 𝑡3=𝑡1×𝑡2≈0.25, and Γ1=Γ×𝑡3≈0.025. Details about how the values of 𝑡1, 𝑡2, 𝑡3, Γ, and Γ1 are chosen are given in Supplemental Material [26], Part I.5.