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。尽管有许多实验旨在揭示聚合物薄膜与光相互作用的机制，但仍然缺乏对固态形态与光物理行为之间关系的全面认识。的H-聚集体模型，这已经成功地描述了旋涂聚（3-己基噻吩）薄膜的光致发光物理，然而，未能占几个关键的光致发光物理性质的亚苯基亚乙烯基和芴基聚合物薄膜，如温度依赖性的光致发光线的形状。该奖项支持研究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，沿着和垂直于聚合物主链。该项目的具体目标包括：1）详细了解链间相互作用（导致离域Frenkel型激发和H-聚集体行为）与链内相互作用（导致Wannier型激发和J-聚集体行为）之间的竞争如何影响分子物理性质。链间与链内竞争可以从吸收和光致发光光谱中的电子振动进展作为激子耦合的函数而改变的方式来理解，激子耦合沿着和垂直于聚合物链、温度以及沿沿着和垂直于聚合物链的空间相关无序的程度。振动的进展，主要来源于无处不在的乙烯基拉伸模式共同几乎所有的π共轭分子，因此作为激子带宽，激子相干长度和广义形态的探针。具体的应用将是聚（3-己基噻吩）组件，其表现为H-聚集体时，从各种溶剂中旋转浇铸，但也作为J-聚集体，当在缓慢冷却的甲苯溶液中自组装。从H-聚集体行为到J-聚集体行为的形态驱动转变的可能性不仅是基本的新奇，而且可以用于器件优化。2)一个更完整的理解激子相干聚合物薄膜，在优化相干传输的目的是利用最近在单链聚丁二炔测量的大相干长度。3)构象无序聚合物链的详细分析，旨在了解无序和电子振动耦合如何合谋创建构象单元并影响物理性质。分析将基于Holstein-品种哈密顿，治疗通过键和通过空间激子相互作用，线性激子振动耦合，并在平等的基础上无序。将采用多粒子近似法将基组减少到便于数值分析的大小，而不牺牲精度。基本激励和他们的稳态频谱签名将使用标准的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。它支持关于由一类长链分子，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。该研究的重点是阻碍理解这些薄膜与光相互作用的机制，光如何被这些材料吸收以及吸收光后电子状态的性质的关键问题。PI的一个关键特征？的方法是考虑电子电荷与分子链振动的相互作用。本计画的重点是研究一个新的模型来描述电子在分子链上和分子链间的沿着运动。特定种类的聚合物的薄膜可用作有机基电子器件如晶体管、发光二极管和太阳能电池的活性材料。该研究项目有助于知识基础，使这些材料能够用于照明，太阳能转换和其他电子设备。软电子设备的商业影响预计将在未来几年内通过柔性显示器，电子标签和固态照明等产品大幅增加。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.