Theoretical Study on the Structures and Nonlinear Optical Properties of Functional Modification Derivatives of Fullerene

Author:Wang Li

Supervisor:chou yong qing

Database:Doctor

Degree Year:2018

Download:177

Pages:132

Size:9310K

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Fullerene cages are hollow spherical symmetric molecules.They usually can be used as efficient π-electron acceptors.Functional modification of fullerenes to regulate their properties has become a necessary mean in the research of fullerene chemistry.Fullerenes have spacious lumen,the metal,rare gas,hydrogen and water molecules can be encapsulated in the fullerene cage.The modification outside of fullerene cage in supramolecular chemistry is one of extensive research topics.The challenges of modification includes capturing spherical surface,driving forces restricted to weak π-π,van der Waals,metal-π coordination.In order to match the convex surface of fullerenes,C20H10 naturally provide concave surface with geometric compatibility,and provide strong electrostatic interaction to form the concave-convex π-π interaction.Embedded fullerene and fullerene supramolecular were widely studied because of these unique properties,and so far the researches of their nonlinear optical(NLO)responses are relatively scarce.This paper adopts density functional theory(DFT),finite field and numerical derivative methods to study the NLO response of embedded,supramolecular and receptor fullerene derivatives,and further devote to study the influence of fullerene size on the NLO response.It will provide provide good reference models to design new molecules with great NLO response,as well as a theoretical foundation for experimental synthesis of such compounds and even further design of NLO material.This thesis mainly studies structure,weak interaction,absorption spectra,NLO properties of embedded,supramolecular and receptor fullerene derivatives.The primary coverage as follows:1.A series of fullerenes with different sizes have been investigated using DFT method to study the influence of fullerene size on second hyperpolarizabilities(γ).The calculation of polarizability α value indicated that the <R2> and α values increase linearly as the fullerenes every increase by 12 carbon atoms.This linear relationship between fullerene size and αvalues provide a new method to improve NLO properties.On the other hand,the γ values depend linearly on the size of the fullerene cage.2.Eight complexes formed by the non-covalent modification of fullerenes were studied by using the DFT theory to study the influence of fullerene size on first hyperpolarizabilities(β)of fullerene/corannulene complexes based on the above work.Fullerene size plays a vital role in the stabilities of these complexes.The aromatic rings of corannulene were inclined to stacking with the aromatic rings of fullerene spheres with identical carbon numbers on account of maximizing shape complementary.For fullerene/bowl supramolecular complexes,as fullerene volume increases,the polarizability value increases gradually.3.Metallofullerene/corannulene complexes have been studied using DFT method based on the above work,with the aim to explore the influence of doping position of Li+ and Li atom on the β values of these complexes,which are selected from work 2.The doped inner complexes display larger β values with respect to C20H10/C60.It is due to that Li+@C60 and Li@C60 show enhanced electron acceptability as compared to pristine C60.Specifically,C20H10/Li C60,related to the easily polarizable excess electron,exhibits larger β value with respect to its inner isomer.Excess electron has large NLO responses and the excess electron has played a crucial role to enhance the β values.4.The successful synthesis of(H2)2@C70 and(H2O)2@C70 provide the first light of morning to synthesize(HF)2@C70.Herein,with the aim to provide a quantum chemical prospective of(HF)2@C70,the comparative studies of hydrogen bonding,electronic structure,weak interaction,absorption spectrum,α and γ values of the H2,H2 O and HF monomers encapsulated inside C60 and C70 have been performed using DFT method.Endohedral C70 possesses the larger γ values with respect to that of endohedral C60.It is due to that larger fullerenes possess larger density amplitude and longer distance as compared to smaller fullerenes.5.Based on the above research,this work to continue to study the Fullerene C60 covalent modification derivatives.Novel NLO chromophores have been reported based on covalent modification of fullerene cage,where N,N-diethyl amine(DMA)as electron donor.The structures,electron absorption spectra and the β values of theses compounds were studied by DFT method.Results show that with the increased number of DMA substituents,the transition energies of electronic excited states gradually decrease,and absorption spectrum wavelength red shift.It put forward an idea for the first time that the number of charge transfer paths has large influence on second order NLO properties.As charge transfer paths increase,β values would increase greatly.