【作者】 唐金龙；

【导师】 刘杰；

【作者基本信息】 四川师范大学 ， 凝聚态物理， 2004， 硕士

【摘要】 本文研究的对象为聚苯胺的完全氧化态，一种导电聚合物。导电聚合物的导电机理不同于金属，也不同于无机半导体。自由电子是金属的载流子，电子或空穴是无机半导体的载流子，然而导电高聚物的载流子是孤子、极化子和双极化子等。由于导电高聚物具有π电子共轭结构，因此，导电高聚物都具有快速响应(10^-13s)和高的三阶非线性光学性质。由于导电高聚物具有特殊的结构和优异的物理化学性能，使得它们在能源（二次电池、太阳能电池和固体电池），发光二极管（LED），传感器，隐身技术以及生命科学等方面都有诱人的应用前景。研究导电高分子材料的电学、磁学和光学等方面的理论日显重要。本文对聚苯胺激子的一些性质进行了研究。 本文的理论基础是准一维体系的电子结构理论，这一基础理论建立在一维的Peierls不稳定性的基础之上，准一维体系理论给出了导电聚合物中的孤子、极化子、激子等概念，并成功地解释了以这些“粒子”为载流子的导电现象。在此基础上，苏武沛、Schrieffer和Heeger等的合作建立了著名的SSH模型用以解释聚乙炔的电子结构和一维的Peierls相变。许多学者也将SSH模型推广到聚苯胺的研究中，如Ginder、Baranowski等，但现有的理论几乎都没有考虑电子相互作用这一强关联因素，尤其是长程库仑力的影响被忽略。显然，这对于激子的复合与湮灭的研究是个缺陷。我们认为有必要考虑电子相互作用。 首先，我们在聚苯胺的Baranowski-Büttner-Voit（BBV）理论模型基础上，加入了长程（计入至第四次近邻）电子—电子相互作用项，对聚苯胺激子静态进行自洽变分计算，对体系的电子结构、键序波、芳环扭角、能隙和能带进行了研究，参照实验结果确定了电子相互作用强度参量。发现引入电子—电子相互作用后，聚苯胺静态激子的性质受到影响，该聚合物的键序波、芳环扭角和电子中文摘要结构发生了变化，而且在理论吸收谱的低能端出现了明显的二特征吸收峰（1.0 ev和1.5 ev附近），这一结果与实验数据很好的吻合，从而这一点表明我们所考虑的因素是合理的。我们的模型参量为:近邻格点电子相互作用强度作0.75 eV，同一格点的电子相互作用强度卜1.5 eV。 进而用上述修正的BBV模型，我们对聚苯胺激子的复合湮灭过程进行了半经验的分子动力学模拟。结果表明，大约在900 fsec之后激子复合过程结束，电子结构返回到二聚化状态，体系的键序波、芳环扭角等回到基态的二聚化状态。并且，体系的二特征吸收峰在此时也己完全消失。这一现象与实验观察到的短寿命光诱致吸收峰结果相似，但在时间上900 fsec短于实验的100 msec。据此我们推断实验上聚苯胺激子复合过程开始前有约为几十个msec的稳定期。 我们的工作表明，扩展的BBV模型能再现聚苯胺体系的大量实验数据，可以对聚苯胺的各种氧化态作进一步研究，也可以推广到其他的类聚苯胺的准一维体系中去。更多还原

【Abstract】 The present work studied an oxidized form of polyaniline, a conducting polymer. Mechanism of conducting polymers is different from metals and semiconductors. Unconstrained electrons are voltaic carriers of metals, and electrons or holes are carriers of inorganic semiconductors, while conducting polymers’ carriers are kinks, solitons, bisolitons or excitons etc. Polymers can be used for energy source (recharge batteries, solar batteries and solid batteries), light emitting diodes (LED), sensors, technology of shelter and life sciences etc., for the particular structures and excellent properties of physics and chemistry. It is important that the theoretical study works of electricity, magnetics and optics for conducting polymer materials. In present work, we studied some properties of biexciton in polyaniline.Theoretical foundation of the present work is theories of electronic structure in one-dimension systems, which is established on the Peierls unstable properties of ID systems. The theories showed us concepts of kinks, solitons, excitons of conducting polymers, and successful explained the conducting phenomenons of these "particles" as carriers. W.P. Su, Schrieffer and Heeger founded the famous SSH model and explained the electronic structures of polyacetylene and the Peierls phase-transform of ID systems. Many scholars generalized the SSH model to polyaniline, such as Ginder, Baraniwski etc. But electron-electron interactions were neglected in those theoretical works, especially influence of the long-range Coulomb force. It is a flaw to study recombination of excitons. So we figured that the influence of the electron-electron interactions must be considered in our work.Added an electron-electron interaction (up to the fourth neighbor) term to the Baranowski-Buttner-Voit (BBV) model for polyaniline, we carried out a self-consistent-variation calculation for an biexciton in the pernigranlilne-base polymer, in order to confirm the model Hamiltonian. The results showed that two peaks (near l.OeV and 1.5eV) appeared in the calculated optical absorption, besides the reproduced electronic structure, bond order wave (BOW) and ring-torsion angles.This result is consistent with the experimentally observed features of short-life. That shows our model is reasonable. The parameters of the extended BBV model are as follows: the near neighbor interaction intension F=0.75eV and the coefficient of the Hubbard term U=1.5eV.Based on above model, molecular dynamics simulation was used to study recombination process of an exciton in the polymer. The results showed that the excitons were completely recombined after 900 fsec and the geometry structure of the polymer such as the BOW and the ring-torsion angles returned to the ground states, which were the dimerization states. Comparison with the experimentally observed life time -100 msec, the recombination time 900 fsec is quite short. Thus we suggested a stable period of dozens msec for the PNB excitons.Our work shows that the extended BBV model can reproduce most observed data of the polymer. More works can be done on the other oxide forms of polyaniline. And the method can be generalized to other quasi-one dimensional systems.更多还原