Theoretical Investigations On The Structure And Properties Of Novel Molecules Constructed From Modified Open-cage Fullerenes

To meet the miniaturization of electronic devices,the exploration and development of innovative molecular-level electronic components（molecular wires,diodes,switches,transistors and memristors）has been the continuing popular subject.Between them,the design and development of high-performance molecular switches,which are crucial in the process of composing molecular circuits,is an essential part of the field of molecular electronics.With a large number of conjugated electrons,fullerenes and their derivative systems have multiple potential applications in the development and design of novel molecular devices.In this thesis,we theoretically designed open-cage fullerene systems modified by alkali metals and salts,and first analyzed the effects of alkali metals on the structure and nonlinear optical properties of open-cage fullerenes through the modification of different alkali metals(M⁺@C₅₀N₅H₅)M?^-（M=Li、Na;M?=Li、Na、K）;next,the modulation of the external electric field（EEF）on the structure,chemical bonding and optoelectronic properties of the system was investigated theoretically using the open-cage fullerene(Na⁺@C₅₀N₅H₅)Cl^-modified by sodium chloride salt as an example.In this thesis,based on the open-cage fullerene(C₅₀N₅H₅)system,respectively,two aspects of the research work were investigated as follows:1、We have designed and investigated the structural and nonlinear optical properties of the series of novel alkalides(M⁺@C₅₀N₅H₅)M?^-（M=Li、Na;M?=Li、Na、K）.Firstly,the nitrogen atoms of open-cage fullerene C₅₀N₅H₅ by their frontier molecular orbital（FMO）and natural population analysis（NPA）charge cause the strong polarization of the s-electrons of the internal alkali metal,forming a diffuse electron cloud to wrap the external alkali metal atom with alkalides properties.Further research revealed that all of these alkalides have significant first hyperpolarizabilities(β_tot)up to190958 a.u.,where the transition energy?E between the ground state and the excited state is the main factor forβ_tot.2、Based on the above work,we doped Cl^-at the open edge of fullerene and Na⁺inside to obtain a novel molecule(Na⁺@C₅₀N₅H₅)Cl^-with more stable Na Cl doping of C₅₀N₅H₅.Then we investigated the structural features,natural population analysis（NPA）charges,chemical bonding,interaction energies and nonlinear optical properties of(Na⁺@C₅₀N₅H₅)Cl^-under the effects of EEF.The results revealed the interesting changes in the structure after the application of an electric field along the Na Cl axial direction（X-axis）:the increase of the strength of EEF in the positive/negative direction leads to the directional migration of Na⁺to Cl^-and the recombination with ionic bonding characteristics.Where EEF=-86×10^-4 a.u.is the critical electric field（E_c）for the interaction between Na and Cl in(Na⁺@C₅₀N₅H₅)Cl^-,where the geometry,stability,electronic properties and nonlinear optical properties of the molecule under the electric field undergo significant changes.This thesis investigates the structure,chemical bonding and optoelectronic properties of open-cage fullerene modified systems by utilizing strategies such as alkali metals doping and the application of EEF.We hope that the series of work in this thesis will provide a new strategy for the design of molecular switching materials in the field of molecular electronics.