To rival the performance of modern integrated circuits, single-molecule devices must be designed to exhibit extremely nonlinear current–voltage characteristics. A common approach is to design molecular backbones where destructive quantum interference (QI) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) increases the nonlinearity of the energy-dependent tunneling probability near the electrode Fermi energy. However, the dynamic range of such devices remains poor because it is difficult to align the frontier orbitals to the electrode Fermi energy. Additionally, this strategy is often implemented in small molecules where there is substantial through-bond tunneling. In this talk, I will discuss a new chemical design strategy. I will show that the LUMO is decoupled in a series of long molecular wires comprising a central benzothiadiazole unit. As a result, constructive QI between the HOMO and LUMO is suppressed, and destructive QI among the HOMO and strongly coupled occupied orbitals of opposite phase is enhanced. I will present data from STM-break junction experiments demonstrating that the conductance of a 6-nm benzothiadiazole wire can be reproducibly modulated by more than four orders of magnitude. Thus, this design strategy may pave the way towards functional, room temperature single-molecule electronics.

Highly nonlinear transport across single-molecule junctions via destructive quantum interference

ACS Spring Meeting 2021

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