Synthesis And Characterization Of Bilayer And Vacancy Defective Nanographene Molecules

Graphene is a two-dimensional material with a honeycomb monoatomic layer thickness formed by sp2 hybridized carbon atoms bonding to each other,showing excellent physical and chemical properties.Synthetic graphene always has various defects,such as Stone-Wales,edge,line,vacancy,non-hexagonal rings and so on,that these defects play a key role in modulating the properties of graphene.However,the defects in graphene are usually various and it is difficult to achieve precise control of the structure.Nanographene is widely regarded as the molecular model of graphene.Research on nanographene has provided deep insights into the structure-property relationships of graphene.Therefore,we can design and synthesize nanographene molecule with well-defined defect architecture and corresponding intact nanographene molecule by organic synthesis methods to study the effect of the introduction of defects on the structure and properties.Although stable bilayer nanographene assembled by?-? interaction can qualify as molecular bilayer nanographene(MBLG),to the best of our knowledge,such an MBLG has not been obtained in a pure form so far,because the propensity for multilayer stacking of nanographene often results in a dynamic mixture of columnar superstructures with indefinite numbers of layers.The generation of welldefined defects in bilayer nanographene systems,also has been a long-standing challenge.The main research work of this paper is as follows:1.The first bilayer nanographene molecule[C114H24(C6H2(CH3)3)6]2(1)was obtained by introducing six mesityl groups on the periphery of the nanographene molecule C114.The MALDI-TOF mass spectra and NMR spectroscopy confirm the structure of 1,which are remarkably stable,showing no sign of aggregation or dissociation by varying the concentration,temperature,and solvent.The first bilayer nanographene molecule can maintain bilayer structure in the liquid phase and stably exist.2.The first bilayer nanographene molecule with benzene ring vacancy defect was designed and synthesized[C108H30(C6H2(CH3)3)6]2(2)by referring to the synthesis strategy of molecule 1.The MALDI-TOF mass spectra,NMR spectroscopy and singlecrystal X-ray diffraction(SCXRD)confirm that the structure of 2 consists of a unique bilayer structure.We demonstrate that 2 maintains a bilayer architecture in gas phase,solution and solid state.Compared with its defect-free counterpart 1,the photoluminescence intensity of 2 showed a 9.6-fold enhancement,which serves as the first atomically precise case of defect-enhanced fluorescence for in nanocarbons.3.There are only two nanographene molecules with double vacancy defects that have been synthesized.In order to enrich its members,we have designed soluble nanographene molecules with six double vacancy defects,which are mesitylsubstituted C180H114(3a)and dimethylphenyl-substituted C174H102(3b).We tried to synthesize them,but the crystal structure indicated that the obtained oxidative dehydrocyclization product was hexaoctylene 3b' with the same molecular weight.Nanographene molecule containing six double vacancy defects was not successfully synthesized.