Modeling the Optical Properties of Conjugated Polymer Assemblies: Interchain Vs. Intrachain Interactions

该奖项由材料研究部和化学部资助。它支持π共轭聚合物和相关低聚物薄膜与光相互作用的理论研究和教育。尽管许多实验旨在揭示聚合物薄膜与光相互作用的机制，但固态形态和光物理行为之间的关系仍然缺乏全面的认识。h聚集体模型已经成功地描述了自旋铸聚（3-己基噻吩）薄膜的光物理性质，然而，它未能解释基于苯乙烯、乙烯和芴的聚合物薄膜的几个关键的光物理性质，例如光致发光线形状的温度依赖性。该奖项支持研究一种更复杂的聚合物聚集体模型——hj -聚集体模型。与h -聚集体模型不同，hj -聚集体模型考虑了多维激子运动，包括沿聚合物主链方向和垂直方向的激子运动。该项目的具体目标包括：1)详细了解链间相互作用和链内相互作用之间的竞争如何影响光物理性质，链间相互作用导致离域的Frenkel型激发和类h聚集体行为，链内相互作用导致wannier型激发和类j聚集体行为。链间与链内的竞争可以从吸收和光致发光光谱中的振动级数作为沿聚合物链和正方向激子耦合、温度以及沿聚合物链和正方向空间相关无序程度的函数而改变的方式来理解。振动级数主要来源于几乎所有π共轭分子普遍存在的乙烯基拉伸模式，因此可以作为激子带宽、激子相干长度和广义形态的探针。具体应用将是聚（3-己基噻吩）组装，当从各种溶剂中自旋铸时表现为h聚集体，但当在缓慢冷却的甲苯溶液中自组装时也表现为j聚集体。从H-聚合行为到j -聚合行为的形态驱动转变的可能性不仅是一个基本的新奇事物，而且可以用于设备优化。2)更全面地了解聚合物薄膜中的激子相干性，目的是利用最近在单链聚二乙炔中测量到的大相干长度来优化相干输运。3)详细分析构象无序的聚合物链，旨在了解无序和振动耦合如何共同形成构象单元并影响其光物理性质。分析将基于荷尔斯坦-哈密顿量，处理通过键和通过空间的激子相互作用，线性激子-振动耦合，并在平等的基础上无序。将采用多粒子近似将基集减少到可处理的大小，以进行数值分析，而不牺牲精度。基本激励及其稳态谱特征将使用标准数值矩阵技术进行评估。该奖项由材料研究部和化学部资助。它支持理论研究和教育，研究由一类长链分子、聚合物组成的薄膜如何与光相互作用和发光。研究的重点是阻碍人们理解这些薄膜与光相互作用的机制、这些材料如何吸收光以及吸收光后电子状态的性质的关键问题。PI的关键特性是什么？S方法是考虑电子电荷与分子链振动的相互作用。这个项目的一个重点是研究一个新的模型来描述电子沿分子链和分子链之间的行为。特定种类聚合物的薄膜可以用作有机电子器件的活性材料，如晶体管、发光二极管和太阳能电池。该研究项目为这些材料在照明、太阳能转换和其他电子设备上的应用奠定了知识基础。软电子设备的商业影响预计将在未来几年急剧增加，通过产品如柔性显示器，电子标签和固态照明。此外，拟议的活动将通过国际合作加强研究基础设施。

This award is funded by the Division of Materials Research and the Chemistry Division. It supports theoretical research and education on the interaction of thin films of pi-conjugated polymers and related oligomers with light. Despite the many experiments designed to uncover the mechanisms by which polymer films interact with light, a global appreciation of the relationship between solid-state morphology and photophysical behavior is still lacking. The H-aggregate model, which has been successful in describing the photophysics of spin-cast poly (3-hexylthiophene) films, nevertheless fails to account for several key photophysical properties of phenylene vinylene- and fluorene-based polymer films, such as the temperature-dependence of the photoluminescence line shape. This award supports research to investigate a more sophisticated polymer aggregate model, the HJ-aggregate model. Unlike the H-aggregate model, the HJ-aggregate model accounts for multidimensional exciton motion, both along and normal to the polymer backbone. Specific goals of this project include: 1) A detailed understanding of how photophysical properties are affected by the competition between interchain interactions, which lead to delocalized Frenkel type excitations and H-aggregate-like behavior, and intrachain interactions, which lead to Wannier-type excitations and J-aggregate-like behavior. The interchain vs. intrachain competition can be understood from the way the vibronic progressions in the absorption and photoluminescence spectra are altered as a function of the exciton coupling along and normal to the polymer chains, the temperature, and the degree of spatially-correlated disorder along and normal to the polymer chains. The vibronic progressions, sourced primarily by the ubiquitous vinyl-stretching mode common to virtually all pi-conjugated molecules, therefore serve as a probe of the exciton bandwidth, exciton coherence length and generalized morphology. Specific applications will be made to poly (3-hexylthiophene) assemblies, which behave as H-aggregates when spin-cast from various solvents, but also as J-aggregates, when self-assembled in a slowly-cooled toluene solution. The possibility of a morphology-driven transition from H- to J-aggregate behavior is not only a fundamental novelty but can be exploited for device optimization. 2) A more complete understanding of exciton coherence in polymer films, with an aim at optimizing coherent transport by taking advantage of the large coherence lengths recently measured in single-chain polydiacetylene. 3) A detailed analysis of conformationally disordered polymer chains, with an aim at understanding how disorder and vibronic coupling conspire to create conformational units and affect photophysical properties. Analyses will be based on Holstein-variety Hamiltonians, treating through-bond and through-space excitonic interactions, linear exciton-vibrational coupling, and disorder on equal footing. Multi-particle approximations will be employed to reduce the basis set to a tractable size for numerical analysis without sacrificing accuracy. Fundamental excitations and their steady-state spectral signatures will be evaluated using standard numerical matrix techniques. NON-TECHNICAL SUMMARY This award is funded by the Division of Materials Research and the Chemistry Division. It supports theoretical research and education on how thin films composed of a class of long chain molecules, polymers, interact with and emit light. The research is focused on key issues that impede understanding of the mechanisms by which these films interact with light, how light is absorbed by these materials and the nature of the electronic states after absorbing light. A key feature of the PI?s approach is to account for the interaction of electronic charge with vibrations of the molecular chains. A thrust of this project is to investigate a new model to describe the behavior of the electrons along molecular chains and between molecular chains. Thin films of particular kinds of polymers may be useful as active materials for organic-based electronic devices such as transistors, light emitting diodes, and solar cells. This research project contributes to the intellectual foundations that will enable the use of these materials for lighting, solar energy conversion, and other electronic devices. The commercial impact of soft electronic devices is expected to dramatically increase over the next several years, through products like flexible displays, electronic labels and solid-state lighting. In addition, the proposed activities will enhance research infrastructure through international collaborations.