The Effect Of Long-range Correlation On The Optical Absorption Of Organic Polymer

People found accidentally in the sixties and seventies of the last century that low dimensional organic polymer such as polyacetylene after doping can conduct. Since then, people pay strong enthusiasm to the study of organic conductive polymers. Organic conductive polymers can not only reflect the properties of semiconductor and metals, but also can reflect its own non-metallic nature such as the properties of corrosion resistance, ease of processing, etc. Organic conductive polymers is a kind of new materials that can be widely applied to the production and living. Thus, the pursuit of organic conductive polymers becomes a new subject of organic molecular electronics rapidly. After decades of research, people knows deeply of conductive mechanism of the carriers in quasi one-dimensional organic polymers and they researched comprehensively of the special electrical, optical, magnetic properties reflected by organic polymers. The data coming from model calculation matches very well with the experimental data. In recent years, people have successfully developed a variety of organic photoelectric devices.In 1974, the Japanese chemists H. Shirakawa et al, synthesized insulating polyacetylene film successfully. After three years later, H. Shirakawa and American scientists A. J. Heeger improved the conductivity of polyacetylene through doping in it, and polyacetylene became good conductor. From then on, Organic polymer began to challenge the leading position of traditional semiconductor in electronics. The research of semiconductor entered a new period. In 2000, H. Shirakawa, A. G. Mac Diarmid and A. J. Heeger won the Nobel Prize in Chemistry together for their outstanding contribution in the field of organic polymer.The theoretical model of quasi one-dimensional organic polymer that established in the end is the result of many researchers continuing effort. The SSH model established by W. P. Su, J. R. Schrieffer and A. J. Heeger effects well in the study of degenerate ground state polymers. In order to study the non-degenerate ground state polymers, Brazovskii and Campbell introduced the symmetry breaking items firstly and solved the question that the two-phase energy is not equal in cis-polyacetylene. Later, People considered the influence on the electronic energy spectrum of the electronic-interactions based on the SSH model and established the extended SSH model. Theoretical model perfected further. It had a great influence on optical absorption of organic polymers by electronic interactions. In recent years, the long-range electron correlation has been found also has an important influence in studying electronic band structure of multi-electron system. It’s significant on the study of the long-range electron correlation.The major contents and conclusions of this paper were summarized as follows:(1) In the third chapter,We consider the extended Hubbard model that describing electronic interaction and the long-range electron correlation on the basis of SSH model. Under the natural boundary conditions, we calculated the electron wave function. Then, we calculated the optical absorption spectrum of polaron in polyacetylene using the "Fermi golden rule". The optical absorption peak of polaron in polyacetylene causes blue shift for the case of electronic interaction and the wavelength of photon absorbed becomes shorter. However, The optical absorption peak of polaron in polyacetylene causes red shift for the case of the long-range electron correlation. The wavelength of photon absorbed becomes longer. Long-range electronic correlation make optical absorption phenomena more likely to happen. It also can be found that the optical absorption peak of polaron in polyacetylene causes red shift for the case of electric field. With the increasing of electric field intensity, The value of optical absorption peak is about 1.779 e V finally. The energy band structure maintain the stability.(2) In the fourth chapter, We calculated the optical absorption spectrum of exciton and bi-exciton in cis-polyacetylene. We analyzes the corresponding of absorption peak with the transition energy simply. The exciton dissociates into polaron for the case of electric field, causing absorption peak blue shift. But it causes absorption peak red shift of bi-exciton for the case of electric field after dissociating. Finally, We analyzed the effect on absorption peak of exciton and bi-exciton for the case of electronic interaction and long-range electron correlation.In conclusion, Long-range electron correlation weak the effect on the optical absorption peak of carriers in PA of electronic interaction. The effect is significant. Long-range electron correlation can not be ignored in the study of optical absorption properties of polyacetylene.