Extended π-Conjugated Systems:Synthesis And Properties Of 2D Nanosheets And Carbon Nanohoops

Owing to their unique physical and chemical properties,two dimensional(2D)materials,such as graphene,metal chalcogenides,metal oxides,and metal hydroxides have attracted much attention in the past decades.However,most of these nanosheets were synthesized via top-down exfoliation from bulk layered materials,therefore the properties of 2D nanosheets are limited by their bulk precursors and it is difficult to produce 2D materials with high structural or functional tunability.As for the preparation of canbon nanotubes(CNTs),traditional physical methods,such as arc discharge,laser ablation,and catalytic thermal chemical vapor deposition,failed to produce CNTs with high purity,which have seriously hindered their large-scale commercialization.Therefore,it is still a great challenge to synthesize length-and diameter-specified single-chirality CNTs.The bottom-up synthetic approach has emerged as a desirable method.By tailoring the utilized building blocks/linkers to fabrricate 2D nanosheets,their structures and properties can be well tuned.Moreover,bottom-up method has also been utilized to synthesize various π-conjugated carbon nanohoops,the segments of CNTs.Recent years have witnessed the rapid development of π-conjugated conductive 2D metal-organic frameworks(MOFs),as well as π-conjugated carbon nanohoops,which were fabricated through bottom-up strategy.This present thesis focuses on the synthesis and properties of π-conjugated systems,including conductive 2D MOFs and carbon nanohoops.The works in details are as follows:1.A novel nickel phthalocyanine-based 2D MOF(NiPc-MOF)with high intrinsic electrical conductivity was first synthesized via facile coordination reaction and well characterized.Further electrochemical measurements revealed its outstanding OER performance under alkaline conditions,including a quite low onset potential,high mass activity,high TOF value as well as robust durability.The synthesis of NiPc-MOF broadens the structures and applications of π-conjugated conductive 2D MOF materials.2.We developed a novel and efficient three-step synthesis approach,the platinum-mediated assembly and subsequent reductive elimination,to synthesis[8]-,[9]-,and[12]CN nanorings with relatively high overall yields.In addition,their photophysical properties in THF were further experimentally investigated,revealing their unique size-dependent properties.This method may open a new way for the synthesis of[n]CNs and facilitate their further utilizations in bottom-up synthesis of uniform CNTs.3.Two giant n-extended molecular carbon macrocyclic rings,CHBC[8]and CHBC[6],were successfully synthesized via platinum-mediated assembly and subsequent reductive elimination.CHBC[8]represents the largest cyclic conjugated molecular CNT segment ever reported.These CHBC[n]s(n=4,6,8)display different photophysical properties,proton NMR patterns,electronic properties,and photocurrent behaviors,suggesting unique size-dependent properties.DFT calculations reveal that the strain energies of CHBC[n]s can be significantly reduced with an increase in the diameters of the rings.These CHBC[n]s could potentially serve as seeds for the bottom-up synthesis of chirality-specified CNTs.4.The supramolecular interactions between two novel molecular crowns(TCR and HCR)and C60 are investigated,revealing an increasing binding constant with extended π-conjugation synstem.Under light irradiation,C60@HCR and C60@TCR generated significant photocurrents.Transient absorption measurements demonstrated efficient charge transport between HCR and TCR(electron donor)and fullerene(electron acceptor).This study may give the insights for the development of bottom-up synthesis of CNTs and potential applications in photoelectroactive devices.