Curved ?-extended Conjugated System: Synthesis And Properties Of Helical Graphene Nanoribbons And Chiral Carbon Nanorings

Nanocarbon allotropes reveal that the structure and arrangement of carbon atoms significantly affect the properties of the materials.Acquiring nanocarbon with atomically precise structure is the key to developing new functional materials and is also a challenge in the field of nanocarbon science.It is a promising method to prepare nanocarbon with atomic accuracy by means of organic synthesis from the bottom-up.It can even control the structure-property relationship of nanocarbon materials.The chemistry of curved nanocarbon allotropes has been of significant interest to explore the relationship between ? conjugation and molecular geometry,which offers an attractive combination of fundamental problems,potential applications,and aesthetic appeal.The syntheses of graphene nanoribbons(GNRs)and carbon nanotubes(CNTs)are considered as the most promising methods in the preparation of graphene materials with bandgap,and therefore have attracted much attention.Twisting or curved planar GNRs will result in new topological structures,which will affect their optoelectronic properties,and may even induce metal-free magnetism and chirality.Since the first synthesis of narrow planar GNRs though bottom-up organic approach in 2010,research on small graphene sheets has experienced rapid development.However,most of the studies just focused on planar GNRs.There are few reports on curved GNRs,although its unique properties have been previously predicted,such as metal-free magnetism and chirality.At present,the design and synthesis of curved GNRs with precise structural definitions is still a challenging topic in the fields of organic synthesis and materials science.Molecular CNTs,such as carbon nanorings,have received widespread attention since researchers proposed the use of templates to grow precisely structured CNTs.Recent years have witnessed breakthroughs and rapid development in the synthesis of CPP-based nanorings as well as their derived molecules.In these molecules,the distortion from aromatic planarity can induce radially oriented ?-systems and further affect their electronic,optical,self-assembly,and charge-transport characteristics.These unique and interesting carbon nanorings are potentially useful in a variety of optoelectronic and biomedical materials.So far,a number of ?-extended carbon nanorings have been reported,and they exhibit novel physicochemical properties resulting from their fascinating topologies and structures.However,there are still some challenges in the synthesis of ?-extended carbon nanorings and their structural analogs,exploration of their unique properties.In addition,?-extended chiral carbon nanorings have been reported less frequently.This dissertation studied the synthesis and properties of a novel helical GNR and a variety of curved chiral carbon nanorings containing small graphene units.The details are as follows:1.The first example of a longitudinally well-extended carbon nanosolenoid(CNS)material based on curved GNRs was successfully constructed through precise design with rigid and steric precursors(hexaphenylbenzene containing phenanthrene structure and ortho-disubstituted terphenyl).The material has a clear structural definition,including armchair-shaped edges and core structures with a width of-2.7 nm,helical pitch of-0.4 nm and coil angle of 3.028°.CNS showed low optical band gap of 1.97 eV and intense red photoluminescence.Magnetic testing revealed that CNS has a para-magnetism response and complex magnetic ordering behavior at low temperature.Such structurally well-defined ?-conjugated CNS allows for detailed study of its physical properties and may provide an important experimental basis for the development of electronic and spintronic devices containing CNS.2.We have successfully achieved the shortest conjugated sidewall segment of[9,8]SWCNT,the chiral carbon nanohoop[7]CPPNa2,6 by incorporating naphthalene unit into the cycloparaphenylene skeleton.Two emission peaks for[7]CPPNa2,6 can be observed in various solvents,which is possibly due to relaxation from different excited states.Theoretical studies revealed that[7]CPPNa2,6 show moderate strain energy(89.6 kcal·mol-1)and higher HOMO-LUMO energy gap(3.5 eV)when compared with those of[8]CPP and[9]CPP of similar sizes.3.We synthesized a series of novel single-chiral PAHs-containing carbon nanohoops with rigidity and different sizes([n]CPPAn2,6,n=6-8)by incorporating anthracene unit into the cycloparaphenylene skeleton to probe the size-dependent property and chiral resolution.These macrocycles were found to have enriched size-dependent physical,chiral,and(chir)optical properties.Notably,these enantiomers showed strong chiroptical properties and dissymmetry factors(|gabs| and|glum|?0.01 for an enantiomer of[6]CPPAn2,6),which makes them extremely valuable in optically active materials.4.Two novel chiral ?-extended carbon nanohoops consisting solely of anthracenes([4]CAn2,6)which can be regarded as(-)/(+)-(12,4)carbon nanotube segment were designed and synthesized based on modular platinum-mediated cyclization strategy.The new tubular CNT segments exhibit large absorption and photoluminescence redshifts compared to the monomer.Notably,chiral enantiomers with(-)/(+)-helicity of[4]CAn2,6 were successfully isolated by HPLC.These carbon enantiomers are also observed to show strong circularly polarized luminescence(glum?0.1).The results reported in this paper will expand the scope of design and bottom-up synthesis of chiral macrocycles and enrich existing knowledge of their optoelectronic properties.