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。它支持关于聚酰亚胺共轭聚合物及其相关低聚物薄膜与光相互作用的理论研究和教育。尽管有许多实验旨在揭示聚合物薄膜与光相互作用的机制，但全球仍缺乏对固态形态和光物理行为之间关系的认识。H-聚集体模型已经成功地描述了旋转浇注聚(3-己基噻吩基)薄膜的光物理性质，但却不能解释苯乙炔和荧基聚合物薄膜的几个关键的光物理性质，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骨料模型--HJ-骨料模型。与H-聚集体模型不同，HJ-聚集体模型考虑了沿聚合物主链和垂直于聚合物主链的多维激子运动。这个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Frenkel类型激发和H-聚集体行为，以及链内相互作用导致Wannier类型激发和J-聚集体行为。从吸收光谱和光致发光光谱中的振动级数作为沿和垂直于聚合物链的激子耦合的函数、温度以及沿和垂直于聚合物链的空间相关无序程度的函数的方式可以理解链间竞争和链内竞争。振动级数主要来源于几乎所有pi共轭分子普遍存在的乙烯基拉伸模，因此可以作为激子带宽、激子相干长度和广义形态的探测器。将具体应用于聚(3-己基噻吩基)聚集体，它们在各种溶剂中自旋浇注时表现为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。形态驱动的H-聚集体行为向J-聚集体行为转变的可能性不仅是一个基本的新奇之处，而且可以被用于器件优化。2)更全面地了解聚合物薄膜中激子相干，目的是利用最近在单链聚二乙炔中测得的大相干长度来优化相干输运。3)对构象无序的高分子链进行了详细的分析，目的是了解无序和振动耦合是如何协同产生构象单元并影响光物理性质的。分析将基于Holstein变化的哈密顿量，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，以及同等基础上的无序。在不牺牲精度的情况下，将使用多粒子近似来将基集缩减到便于处理的大小，以便进行数值分析。基波激发及其稳态谱特征将使用标准的数值矩阵技术进行评估。非技术总结该奖项由材料研究部和化学部资助。它支持关于由一类长链分子和聚合物组成的薄膜如何与光相互作用并发光的理论研究和教育。这项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态的性质的关键问题。Pi？S方法的一个重要特点是考虑了电子电荷与分子链振动的相互作用。这个项目的一个主要目的是研究一种新的模型来描述电子沿分子链和分子链之间的行为。特定类型聚合物的薄膜可用作有机电子设备的活性材料，如晶体管、发光二极管和太阳能电池。这一研究项目有助于为将这些材料用于照明、太阳能转换和其他电子设备提供智力基础。通过柔性显示器、电子标签和固态照明等产品，软电子设备的商业影响力预计将在未来几年大幅增加。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.