Quantum interference effects (QIE) have become an emerging area in single-molecule charge transport investigation, which represents unique quantum effects with an opportunity for fine tuning the charge transport through molecular building blocks by constructive or destructive quantum interference effects. During the past six years, we carried out a series of single-molecule conductance measurements to investigate the quantum interference effects in the charge transport through various types of molecular junctions at room temperature. Benefiting from the high current sensitivity up to fA level, we obtained the conductance of a cross-conjugated anthraquinone using mechanically controllable break junction (MCBJ) technique, which is considered as the first experimental observation of destructive QIE at single-molecule scale by Prof. Mark Ratner. And then we carried out the systematic experimental investigation of QIE from single benzene ring to four- membered and six-membered graphene-like polycyclic aromatic hydrocarbon molecules with different connectivities. The destructive QIE were also found in the central pyridine ring while the different position of heteroatom in hydrocarbon ring, which leads to the gating of quantum interefernce. One of our recent studies suggested that the destructive QIE appeared in the novel metalla-aromatic system with metal atom involved in the conjugation. Beyond the detection, the fine tuning of destructive QIE will be the next crucial step for the utilizations of QIE in molecular materials and devices. It is found that the QIE could be tuned via the protonation of the azulene core, and electrochemical gating offered possibility of switching anthraquinone between oxidized state with destructive QIE and the reduced one without destructive QIE. Recently, our studies suggested that photo illumination and heating also provide the access to manipulate the destructive QIE of dihydroazulene molecules. More importantly, the distingusihable conductance different from QIE offer the opportunity to detect the reaction kinetics at the single-moleule scale. As a perspective, the molecules with destructive QIE are expected to have high Seebeck coefficient with promising applications for thermoelectric devices, which suggests that the QIE are leading to the unique application in the future design and fabrication of molecular materials and devices.

Quantum interference effects in the charge transport through single-molecule junctions

255th National Meeting (2018)

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