The Effect Of F/O-S Non-covalent Conformational Lock On Molecular Charge Transport

Molecules containing non-covalent conformational locks(NCLs)have excellent charge transport properties and device performance,but their working mechanism at the molecular level has not been elucidated in detail.In this study,five kinds of molecules with NCLs structure were synthesized,and their intramolecular and intermolecular charge transport properties were studied.The main contents are as follows:(1)Three molecules with non-covalent conformational locks were designed and synthesized: 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole(DT-BT),5,6Difluoro-4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole(DT-FBT),5,6bis(hexyloxy)-4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole(DT-OBT).The molecular structure was examined by proton nuclear magnetic resonance spectroscopy,the initial oxidation potential was measured by cyclic voltammetry,and the highest occupied orbital and the lowest unoccupied orbital energy level were calculated combined with its ultraviolet absorbable spectrum.The conductance was further measured by scanning tunneling microscopyconsolidation method(STM-FJ),and the intramolecular charge transport was compared with theoretical calculations.The measured conductance(G)order of the three molecules is GDT-BT < GDT-FB < GDT-OBT,which is inconsistent with the conductance order predicted by tunneling theory.According to the results of electrochemical analysis,UV absorbable spectroscopy and electron cloud distribution analysis,the main reason is that the non-covalent conformational lock embedded in DT-FBT and DT-OBT effectively promotes the intramolecular charge transport.(2)Two molecules containing non-covalent conformational locks were further designed and synthesized: 2-(4’-(methylthio)-[1,1’-biphenyl]-4-yl)thiophene(ST),(2-(3-Fluoro-4’-(methylthio)-[1,1’-biphenyl]-4(ST-F).The molecular structure was verified by proton NMR,and its origin was measured by cyclic voltammetry.The HOMO-LUMO was calculated based on the onset oxidation potential combined with the UV absorbable spectrum.The conductance was further studied by scanning tunneling microscopy-split junction(STM-BJ),and it was found that: ST has two conductance peaks,of which the low conductance peak is molecular It is caused by π-π stacking;while ST-F with higher flatness has only a high conductance peak,indicating that it is a single molecule charge transport.For molecules with non-covalent conformation lock structure,flatness will also affect intermolecular charge transport.transport has an important impact.