Electron-Electron Interactions and the Photophysics of Semiconducting Conjugated Polymers and Single-Walled Carbon Nanotubes

该奖项支持半导体共轭聚合物和单壁碳纳米管的理论研究。该奖项由理论和计算化学项目以及材料理论项目支持。该项目有四个不同的目标。(1)发展了有机发光二极管(OLED)中相反电荷极化子之间电荷转移(CT)反应中与自旋相关的激子形成的综合理论。我们将超越我们以前的工作，即专注于最低的单态和三态激子的相对产额，以确定在广泛的库仑参数、分子结构和分子组分之间的相对取向下每个自旋通道的总产额。(2)发展了双分子三重态湮灭(TTA)的微观理论。(3)我们将获得具有红外光学带隙的PI共轭聚合物的相关电子描述。(4)最后，我们计划建立半导体单壁碳纳米管(SWNT‘s)的激子电子结构和光学非线性理论。我们的研究将包括在Pariser-Parr-Pople和扩展的Hubbard哈密顿量下对pi-共轭分子和聚合物的多体计算。所采用的方法将包括精确对角化、单点和多点参考单点和双点组态相互作用(SCI和MRSDCI)以及密度矩阵重整化群(DMRG)。在OLED中发生的竞争性CT反应的相对产率将在依赖时间的薛定谔公式中确定。我们的重点是开发概念框架，而不是材料参数的定量计算。因此，对电子-声子相互作用的明显忽视是基于这样一种观点，即一旦理解了电子-电子相互作用的影响，就可以嫁接电子-声子相互作用的质量效应。由于在这些体系中存在中等强度的电子-电子相互作用，因此很难理解圆周率共轭体系的光物理。目前的拨款在两种不同类别的碳基半导体中提出了及时而重要的问题。我们将使用最先进的技术来调查这些问题。我们研究OLED中CT反应的确切方法是在平等的基础上处理分子间相互作用和多电子相互作用。对TTA的研究将是构建这一现象的微观理论的首次尝试。对小光学带隙聚合物的DMRG计算将为将这些聚合物和相关聚合物用于发光或光伏器件的可行性提供有价值的信息。对单壁碳纳米管的研究将使人们对它们的激子电子结构和非线性光学性质有新的定性的认识。在过去的二十年里，pi共轭聚合物和分子已经从实验室的好奇演变成了关键的新的光学材料。这里所做的研究将对实验者正在进行的广泛的研究产生强烈的影响，从纯粹的基础科学延伸到应用方面。我们希望回答实验同事们正在探索的几个问题，并鼓励他们冒险尝试新材料合成和新实验。这里的一个关键主题是电子-电子相互作用效应。这是一个至关重要的广泛研究领域。我们预计，在我们的研究中创建的知识库将影响我们对强关联电子系统的总体理解。仅作为一个例子，我们提请注意我们在铜酸盐的非线性光学方面的工作，它的起源可以直接追溯到我们在PI共轭聚合物中的光学非线性方面的工作。最后，这项研究提供了一个极好的机会来培训学生和博士后在材料物理、化学以及有机材料和强相关系统的高级计算物理等科学和技术至关重要的领域。%该奖项支持半导体共轭聚合物和单壁碳纳米管的理论研究。该奖项由理论和计算化学项目以及材料理论项目支持。在过去的二十年里，圆周率共轭聚合物和分子已经从实验室的好奇演变为关键的新光学材料。这里所做的研究将对实验者正在进行的广泛的研究产生强烈的影响，从纯粹的基础科学延伸到应用方面。我们希望回答实验同事们正在探索的几个问题，并鼓励他们冒险尝试新材料合成和新实验。这项研究提供了一个极好的机会，培训学生和博士后在科学和技术关键领域的材料物理、化学和有机材料和强相关系统的高级计算物理。*

This award supports theoretical research on semiconducting conjugated polymers and single-walled carbon nanotubes. The award is supported by the Theoretical and Computational Chemistry Program and the Materials Theory Program. The project has four distinct goals. (1) We intend to develop a comprehensive theory of spin-dependent exciton formation in the charge-transfer (CT) reaction between oppositely charged polarons in organic light emitting diodes (OLED's). We will go beyond our previous work, which was focused on the relative yields of the lowest singlet and triplet excitons, to determine the overall yields in each spin channel for a wide range of Coulomb parameters, molecular structures, and relative orientations between molecular components. (2) We will develop a microscopic theory of bimolecular triplet-triplet annihilation (TTA). (3) We will obtain correlated electron descriptions of pi-conjugated polymers with optical gaps in the infrared. (4) Finally, we plan to construct a theory of excitonic electronic structure and optical nonlinearity of semiconducting single-walled carbon nanotubes (SWNT's).The investigations will consist of many-body calculations within the Pariser-Parr-Pople and extended Hubbard Hamiltonians for pi-conjugated molecules and polymers. The approaches taken will include exact diagonalizations, singles and multiple-reference singles and doubles configuration interaction (SCI and MRSDCI), and the Density Matrix Renormalization Group (DMRG). The relative yields of competing CT reactions that occur in OLED's will be determined within a time-dependent Schroedinger formulation. Our emphasis is on developing conceptual frameworks, and not on quantitative calculations of materials parameters. Thus the apparent neglect of electron-phonon interactions is based on the argument that their qualitative effects can be grafted on once the effects of electron-electron interactions are understood.Understanding the photophysics of pi-conjugated systems is difficult, because of the moderately strong electron-electron interactions in these systems. The present grant poses timely and important questions, in two different classes of carbon-based semiconductors. We will use state of the art techniques to investigate these questions. Our exact approach to the study of CT reactions in OLED's treats intermolecular interactions and many-electron interactions on equal footing. The research on TTA will be the first attempt to construct a microscopic theory of this phenomenon. The DMRG calculations on the small optical gap polymers will give valuable information on the feasibility of utilizing these and related polymers in emissive or photovoltaic devices. The research on the SWNT's will give new qualitative insight on their excitonic electronic structure and their nonlinear optical properties.During the past twenty years pi-conjugated polymers and molecules have evolved from laboratory curiosities to key new optical materials. Research done here will have strong impact on a broad range of investigations being pursued by experimentalists, extending from purely fundamental science to applied aspects. We hope to answer several questions being probed by experimental colleagues, as well as influence them to venture out and try new materials synthesis and new experiments. One key theme here is electron-electron interaction effects. This is a vital broad area of research. We expect that the knowledge base created in our studies will impact our understanding of strongly correlated electron systems in general. As merely one example, we draw attention to our work on the nonlinear optics of cuprates, whose origin can be traced directly to our work on optical nonlinearities in pi-conjugated polymers. Finally, the research offers an excellent opportunity to train students and postdoctoral associates in the scientifically and technologically vital areas of materials physics, chemistry and advanced computational physics of organic materials and strongly correlated systems.%%% This award supports theoretical research on semiconducting conjugated polymers and single-walled carbon nanotubes. The award is supported by the Theoretical and Computational Chemistry Program and the Materials Theory Program. During the past twenty years pi-conjugated polymers and molecules have evolved from laboratory curiosities to key new optical materials. Research done here will have strong impact on a broad range of investigations being pursued by experimentalists, extending from purely fundamental science to applied aspects. We hope to answer several questions being probed by experimental colleagues, as well as influence them to venture out and try new materials synthesis and new experiments. The research offers an excellent opportunity to train students and postdoctoral associates in the scientifically and technologically vital areas of materials physics, chemistry and advanced computational physics of organic materials and strongly correlated systems.***