Theoretical Study On The Doping Influence Upon The Geometries And Electronic Properties Of Conducting Polymer Chains

In this paper, the issue of doping influence on the organic conducting polymers that have attracted great concern over the past three decades, was investigated by means of density functional theory (DFT). We calculated the geometries and electronic properties of polybenzimine (derivative of polyanline) doped with different dopants as a function of various doping level, and that of iodine doped poly(p-phenylene sulfide). The doping effects on the electrical conductivity of conducting polymer materials were analyzed in detail by optimizing the geometries of monomer, oligomer, and corresponding polymer. As followed are the main contents:In chapter1, the research progress, conductive mechanism, application and design principles of the organic conducting materials. The related research on the organic conducting polymers has become a star project associated with novel organic functional materials, which can be ascribed to the excellent conducting property, unique optical property, and potential application prospect of the organic conducting polymers. Furthermore, the content and significance of our research work were also introduced in this section.In chapter2, the detailed computational methodologies were given, namely, density functional theory, while several significant analysis methods were elucidated, including atoms in molecular (AIM) theory, nature bond orbital (NBO), time-dependent density functional theory (TD-DFT) as well.In chapter3, the geometries and electronic properties of oligo-benzimine doped with different alkali metal salts at various doping concentration were computed using the density functional theory at the B3LYP/6-31G(d) level. On the basis of the optimized structures, the geometries and electronic character of their corresponding periodic polymers were calculated at the same level as well, the topological analysis of electron density, natural bond orbital analysis, and the total density of state and projected density of state were also illustrated. According to analysis results, it indicates that the introduction of dopant gives rise to the charge transfer along or between the polybenzimine chains, which makes the significant increase in the electrical conductivity of polybenzimine, ranging from the insulator in eigenstate to the potential semi-conductor in doped state. In the case of the same dopant, the electronic conductivity increased with the doping level raised, whereas the stronger of the alkality derived from the alkali metal, the more amount of the charge transfer, in other words, the change in the electronic property of polybenzimine chain was the most prominent when KC1acted as dopant, comparing with NaCl and LiCl. Consequently, the introduction of dopant is one of the principle methods in an attempt to enhance the electrical conductivity of organic conducting materials. The KCl-doped polybenzimine investigated at an appropriate doping level maybe a potential candidate for conducting polymers.In chapter4, we investigated the geometries and electronic properties of iodine doped poly(p-phenylene sulfide), using the density functional theory with the B3LYP method at the6-31G(d) level, except the iodine atom, for which we employed the standard LANL2DZ basis set. We explored the geometries and electronic properties of doped poly(p-phenylene sulfide) in terms of electron density difference plots, Mulliken charge analysis (MPA), orbital composition analysis, absorption spectra, density of state (DOS)and projected density of state (PDOS). Poly(p-phenylene sulfide) is an insulator in its eigenstate, due largely to the quite high oxidation potential (6.3eV), while its electronic conductivity increased significantly after doping with iodine, which results from the charge transfer generated along or between the polymer chains. Based on the research outcomes, the probability of charge transfer between polymer chains is much more than that along the polymer chain. Besides, the amount of charge transfer increased with the elongation of polymer chain. What’s more, the distortion of the polymer structure reduced with the main chain extended, which renders the charge transfer tend to happen between polymer chains. Owing to the quite narrow band gap (1.278eV), iodine-doped poly(p-phenylene sulfide) is an outstanding organic conducting material.