Theoretical Studies On The Structure And Nonlinear Optical Properties Of Doped Fullerene C₆₀(C₅₉M And C₅₈M’)

Fullerenes and their derivatives have unique geometric structures and highly delocalizedπelectrons,so they are widely used in the fields of electricity,magnetism,optics and biomedicine.Chemically modified fullerenes break the original centrosymmetric structure and have potential applications in the field of high-performance second-order nonlinear optical（NLO）materials.In this thesis,we do a detailed design and systematically theoretical calculation on a series of heterofullerenes,which are one or more carbon atoms get replaced by a non-carbon atom,and compare the first hyperpolarizability of these fullerenes.We try to investigate the relationship between heterofullerenes’structures and second-order NLO properties by theoretical calculation.Wish this work could provide reliable theoretical basis for the nonlinear optical material studies.The specific work is as follows:1.Based on the highly symmetric C60,we used three transition metal atoms Co,Rh and Ir as heteroatom doped on fullerene to build C₅₉Co,C₅₉Rh and C₅₉Ir.From the molecular structure analysis,the bonds length between the heteroatoms and the three connected carbon atoms are longer than the carbon-carbon bonds on C₆₀0 and the three heterofullerenes have deformations from C₆₀.Results from natural population analysis（NPA）charge and the frontier molecular orbital show that the charge transfer between heteroatom and carbon atoms on the carbon cage exists in the three heterofullerenes.To our satisfaction,they all have high NLO response,especially,C₅₉Ir has the highest first hyperpolarizability.2.The literatures show that two adjacent carbon atoms of fullerene can be replaced by metal and some nonmetal atoms.Based on our former research,we chose Ir,Pt,Si and S as hetero atom,which are metal and nonmetal,respectively,and used one heteroatom to replace two carbon atoms on the[6:6]ring to build heterofullerenes C₅₈M’（M’=Ir,Pt,Si and S）.Relevant Investigation on optimized structures,frontier molecular orbital analysis,NPA charge and second order nonlinear optical properties of C58M’were carried out.It is worth noting that compared with traditional fullerenes,the NLO response of heterofullerenes get improved,among which,the first hyperpolarizability of metal doped fullerenes is better than that of nonmetal doped fullerenes.In addition,the two-level expression analysis point out that the metal-doped fullerenes have smaller transition energy and larger transition dipole moment,which proves the NLO response of metal doped fullerenes are better than nonmetal doped fullerenes.