Theoretical Computation And Investigation On Three Dimensional Aromaticity Of Small Fullerene Cages

Fullerenes are among the important clusters in field of the research and application for nanoscale physics,people have been doing much work to investigate the properties of the typical cage like fullerene,i.e.the C₆₀since it was discovered and synthesized in the 80s of last century and now it's tried widely at area like material and medical research.C₆₀was an representative choice for theoretical research because of its structural specialty,while small fullerene cages make it the same good representation and necessity for research of the series due to diversity of the cages with different numbers of atoms.Generally small fullerene cages come with reduced radius thus are more likely to be influenced by the tension of constitutive rings among the cage,leading to changes of many properties.Inspired by the two kinds of typical structure,i.e.benzene and C₆₀,in this work we focus on the aromaticity and take C₂₄,C₂₂N₂and other small fullerenes consist of24 atoms as targets,which belong to the transitional cases between the two dimensional and three dimensional molecules with high symmetry,hoping to draw out the relations behind the aromaticity of two dimensions.Aromaticity remains fascinating owing to the diversity and controversy of the theory,it was firstly proposed to describe the stability of ring molecules in chemistry and now widely used in many cases in terms of related properties.Commonly there are investigations on two dimensional cases like rings or plane molecules with many rings,as for three dimensional molecules,method targeting at C₆₀was routinely employed,then less discussion about relations or transition of the two rules was reported.In this work we developed another starting point after going through vast discussions about it.Among different researches,the consideration of delocalized electrons in aromatic molecules can be a good choice to connect the aromaticity of two dimensions and map out the current which indicates the aromaticity.In this work we investigated the induced current of molecules caused by external magnetic field,with the strength and distribution of current it's possible to analyze the aromaticity of different directions,also we introduced different numbers of N atoms to substitute C atoms and observed the changes of the current and aromaticity.Besides,the exploring of potential relations of aromatic rules for two dimensions,i.e.two dimensional and three dimensional was quiet a new breaking piont of the subject.The arrangement of this work concentrated on calculations and analysis of C₂₄molecule series,before that the nanotechnology and C₆₀fullerene was introduced,also the structure of C₂₄molecule series was discussed.Then came a review of the concept and measure of aromaticity as well as the computational theories,we mentioned ICSS(Iso-chemical-shielding surfaces)and ACID(Anisotropy of the induced current density)method,the former rendered the NMR calculation in three-dimensional space,while the latter presented the distribution of induced current within molecules caused by external magnetic field,both methods are frequently used later with more details for the analysis of C₂₄molecule series.Discussion on C₂₄molecule series was conducted using ICSS and ACID method respectively,first we applied the ICSS method to investigate the aromaticity of C₂₄and C₂₂N₂and concerned the results of coexisted aromaticity in different directions.Then we resort to ACID method for more efficiency and separation of orbital contributions that ICSS method provided less.The result obtained using ACID and ICSS method gave information about aromaticity in many parts or orientation inside or outside the cages,indicating partially existence of aromaticity.Finally the discussion on C₂₀N₄and C₁₈N₆was completed in less pages and focusing on the changes in delocalized electrons that influenced by the substitution N atoms,the aromaticity and the relation of the whole and partial molecule was considered corresponding to the theory interpreting the typical two dimensional and three dimensional cases from the view point of electron numbers.Thus we presented another description and possible relations between the classical two dimensional and three dimensional cases,i.e.the transitional cases for the completeness of the series,and provide another way of thinking for theoretical research in such field.