Synthesis And Properties Of Multinuclear C-HBC Stepped Graphene Nanoribbons

Among many organic optoelectronic materials,planar graphene nanoribbons have attracted extensive attention due to their high thermal conductivity,low resistivity,good transparency,good ductility,and high electron mobility.In addition to the above characteristics,the corresponding non-planar nanoribbons have unique optoelectronic properties due to their unique twisted structures.In the meantime,the introduction of helicene structure onto non-planar graphene nanoribbons will induce increased solubility which makes such unique helical non-planar nanoribbons of atomic precision potential candidates in important applications such as semiconductor transistors,organic photovoltaic cells,chiral optics,etc.The twisted hexabenzocoronene(c-HBC)molecule has always been a research hotspot by scientists due to its unique biconcave structure and electrical properties.This unique biconcave structure can interconvert in solution and maintain unchanged in solid state.On the one hand,such contorted structure helps to weaken intermolecular stacking,improve solubility and solution based processability;Complementary stacking enables these molecules to have higher electrical conductivity and photon transport properties.In this thesis,contorted hexabenzocoronene is used as the basic building unit to expand into one-dimensional oligomeric hexabenzocoronene nanoribbons,which include two kinds of polyconcave nanoribbons,a dual-core c-HBC dimer and a tri-core c-HBC trimer.The design,synthesis and their optoelectronic properties were described.The full text is divided into five chapters:Chapter 1 introduces the basic characteristics,classification,synthetic methods,applications,research progress and challenges in the field of graphene nanoribbons,the origin and development of helicene compounds,and their common applications.The significance and program strategy of the research topic of this thesis are also discussed.Chapter 2:Synthesis and characterization of binuclear c-HBC ladder molecules.A"skeleton construction and post-modification"strategy was adopted.Firstly,the problem of poor solubility of synthetic intermediates and products was solved by introducing alkoxy chains on the octacene skeleton,and a dimer containing alkoxy chains was successfully synthesized.But no crystal was obtained,and the specific structure of the molecule could not be determined.Alternatively,the alkoxy chains on the skeleton were removed and a tert-butyl groups were introduced onto the peripheral benzene rings,and the crystal was successfully obtained.The structure consisting a ladder shape is the same as what we expected.The angles of the two staircases are22.58~o and 18.08~o,respectively.The photoelectric properties were further investigated by UV-Vis absorption spectrum,fluorescence emission spectrum and cyclic voltammetry.Chapter 3:Synthesis and characterization of helical c-HBC trimers.Different product configurations were obtained by the same synthetic strategy,the trimer was determined to be a helical structure by crystallography.We predict that the resolved chiral helical nanoribbons should have potential applications in chiral optics.The photoelectric properties were further studied by UV-Vis absorption spectroscopy,fluorescence emission spectroscopy and cyclic voltammetry.Chapter 4:Synthetic route and progress on the synthesis of trinuclear c-HBC ladder trimer was described.To obtain a ladder-type trimer,a step-by-step ring closure strategy was pursued instead of the one-step ring closure method.Chapter 5:Summary and outlook.