Detection And Manipulation Of Intramolecular And Intermolecular Charge Transport Using Mechanically Controllable Break Junction Technique

Interamolecular and intermolecular charge transport in organic electronic devices plays an important role in organic electronic devices.The investigation of the intramolecular and intermolecular charge transport properties of π-conjugated molecules not only enables the fully understanding of charge transport mechanism in aggregation state,but also acts as the guidance for the development of high-performance organic electronic devices.In previous studies,the investigation of intramolecular and intermolecular charge transport properties is mostly in the aggregation state of π-conjugated molecules.However,owing to the presence of intermolecular and intramolecular interactions and lattice vibrations around molecules in aggregation state,it is hardly to distinguish and investigate the intrinsic properties of intramolecular and intermolecular charge transport.Compared with the convertional measurement techniques,mechanically controllable break junction(MCBJ)technique is one of single-molecule electrical techniques with high mechanical stability,which is widely employed in the characterization of charge transport through single-molecule and supramolecular junctions,thus providing a unique opportunity for distinguishing the intramolecular and intermolecular charge transport process.Besides,owing to its high sensitivity and time resolution,MCBJ technique has also been applied in probing the reaction kinetics,which offers a novel platform for the quantitive investigation of intramolecular and intermolecular charge transport properites.Accordingly,we carried out the systematical works to explore the intramolecular and intermolecular charge transport properties of πconjugated molecules.The main content and key results of this thesis are shown as follows:1.We studied the effect of Lewis acid-base interactions on the charge transport properties of triarylboron compound in single-molecule junctions.Triarylboron compound is one of the most important organic photoelectric materials,and the electron-deficient boron atom is subject to Lewis base through strong Lewis acid-base interactions,which will change the molecular structure and the intramolecular charge transport properties.We investigated the gating effect of side chain B-F Lewis acid-base interactions on the charge transport properties of main chain and developed a new precision modulation method based on B-F interaction.2.We investigated quantum interference effects on the charge transport of thiophene derivatives.Quantum interference effects of thiophene central ring with different connectivities were studied by MCBJ technique.We found that the conductance of thiophene derivative with 2,4-connectivities is more than 20 times lower than the other three molecules,which was attributed to the destructive quantum interference effect in thiophene derivative with 2,4-connectivities.3.We demonstrated that charge transport through intermolecular and intramolecular paths in thiophene derivatives could be distinguished and investigated at the single-molecule level.It is found that the the conductance of single-molecule junctions through intramolecular path decreaed exponentially with the increasing of molecular length.In contrast,the conductance of dimer junctions intermolecular path is almost independent of the conjugation pattern.The difference between intramolecular and intermolecular charge transport properties leaded to the transition of dominant charge transport path of molecules from intramolecular to intermolecular when the conjugation increased.It is also found that dimer junctions with different molecular structures showed similar conductance but different binding probabilities due to the different binding energies,which is also supported by density functional theory calculations.