Single-Molecule Study Of Intramolecular And Intermolecular Charge Transfer

The limit to miniaturization of electronic devices is to reach the single-molecule level,which is difficult to achieve based on traditional silicon-based techniques due to quantum effects.Therefore,the “bottom-up” fabrication of molecular integrated circuits by means of molecular electronics provides a new opportunity for further miniaturization of electronic devices.In addition,molecular electronics also provides an effective means for exploring chemical reaction mechanisms,nano-electrocatalysis,isomer recognition,biological detection,and the study and discovery of physical effects at the nanoscale.Such great research value attracts scientists to continuously explore and make great progress in this field.Charge transport in single molecule devices,including intramolecular and intermolecular transport,is the core of molecular electronics research,and is of great significance.Quantum interference(QI)has attracted great attention in recent years because of its great role in tuning charge transport in molecular devices.In order to have a deeper understanding of the relationship between QI effect and molecular structure,we conducted a systematic investigation on how two N-atoms synergistically modulate the QI effect in molecular devices by scanning tunneling microscopy-break junction(STM-BJ).It should be emphasized that in addition to intramolecular charge transport,intermolecular charge transport is also crucial for the fabrication of molecular integrated circuits,which is conducive to inhibiting the tunneling current between electronic components and thus protecting integrated circuits.Furthermore,it plays an important role in chemistry,biology,and organic electronics.Therefore,we study the charge transport behavior based on the intermolecular π-π interaction and metal-metal interaction.The specific conclusions are as follows:1.We have designed and synthesized a series of m-OPE derivatives with double N-substitution,and systematically investigated the synergistic gating effect of double N-substitution on destructive quantum interference in m-OPE molecular junctions using STM-BJ technique.The conductance measurements show that the molecular conductance is strongly correlated to the relative positions of the two N atoms.By altering the positions of two N atoms in the central ring with respect to the connecting sites,the molecular conductance can be tuned by more than one order of magnitude.Theoretical analysis,including magic ratio theory,orbital rule and transmission simulations,reveals how the two N atoms synergistically modulate the molecule conductance between destructive QI and constructive QI states.Remarkably,addition of a second N atom does not simple reinforce the effect of the first;in contrast,it may completely cancel the effect of the first.This work reveals the synergistic gating mechanism of double N-substitution on the destructive QI,and paves a path towards utilization of heterocyclic aromatic hydrocarbons in molecular electronics.2.We have designed and synthesized a series of anthracene derivatives with single anchor groups,and investigated the ability to fabricate single-stacking junctions for charge transport by STM-BJ technique.The conductance measurements show that only the molecules with rigid planar structure and halogen atom substitution successfully fabricated the single-stacking junctions and then realized effective charge transport.Meanwhile,by changing the substituted halogen atom in the anthracene,we were able to achieve more than 3-fold conductance modulation for single-stacking junctions.Theoretical simulation shows that molecules with rigid planar structure are more likely to form effective π-π stacking,and doping halogen atoms can enhance the interaction between molecules,which promote charge transport through space.In this work,the relationship between the molecular structure of anthracene derivatives and the intermolecular charge transport has been deeply understood at the single-molecule level,which provides fundamental guidance for development of the molecular devices based on free π-π interaction,and is also beneficial to the construction of more efficient organic optoelectronic devices based on anthracene functional units.3.We have designed a series of Pt(II)polypyridine complexes with single anchor group.The intermolecular charge transport and third-order nonlinear optical properties of these complexes have been systematically studied by STM-BJ and Z-scan techniques.Single molecular conductance measurements show that the single-stacking junctions could be fabricated based on the strong intermolecular Pt(II)-Pt(II)and π-π spatial interactions.This is the first report of charge transport based on the intermolecular interaction of Pt(II)complexes.In addition,the Z-scan results show that the strong intermolecular interaction of the complexes produced an obvious anti-saturation absorption signal,which shows the application prospect in the field of high-energy protection.This work provides a new strategy for the fabrication of efficient charge transport devices and high energy protection materials based on the intermolecular interactions of organometallic complexes.