Optical Excitations in Supramolecular Assemblies of Conjugated Oligomers and Polymers

作为有机基场效应晶体管、发光二极管（oled）和太阳能电池的活性材料，π共轭聚合物薄膜及其后代低聚物继续受到广泛关注。尽管许多实验旨在揭示低聚物/聚合物薄膜与光相互作用的机制，但缺乏对固态形态和光物理行为之间关系的基本认识。在这个更新建议概述了一个策略，从理论上研究一类新兴的基于低聚对苯乙烯（OPVn）和低聚噻吩（OTn）衍生物的超分子组装。侧基和端基功能化诱导了自组装纳米结构的手性和氢键，包括螺旋棒聚集体、玫瑰花形聚集体和二维片层。这些结构中的许多采用p-堆叠基序，以补充在未取代的OPVn和OTn分子的晶体和薄膜中发现的更常见的人字形排列。具体目标包括：详细了解激子离域、激子-声子耦合和无序对手性聚集体光激发和光发射态的影响。丰富的螺旋棒聚集体光谱数据，包括稳态吸收、光致发光、圆二色性（CD）和圆偏振发光（CPL），允许严格测试具有各种静态无序场景的理论模型。在opvn基螺旋棒聚集体以及手性聚噻吩薄膜中观察到的CPL不对称幅度随波长增加而不寻常地消失的全球解释是寻求的。在一系列环氧乙烷末端覆盖的OTn纤维聚集体（n=5,6,7）中，对增加寡聚物长度对激子带宽的有害影响进行了强有力的理论解释。带宽在聚合物极限下的表现对于理解具有重要技术意义的区域规则聚（3-烷基噻吩）薄膜中的能量传输和光学性质至关重要。螺旋棒聚集体快速皮秒能量输运的精确模拟，以及光隙以上激发后发射谱线形状的时间演变。发射谱线形状提供了有关高能发射态的宝贵信息。分析将基于荷尔斯坦哈密顿量，处理激子相互作用，线性激子-振动耦合，以及点缺陷和结构缺陷对同等基础的影响。将采用双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。激子极化子及其稳态光谱特征将使用标准数值矩阵技术进行评估。激子输运研究将采用泡利主方程。拟议活动的更广泛影响将主要通过加强对技术上重要的材料类别的理解来感受到，可能导致改进的有机发光二极管和有机太阳能电池的新设计策略。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，甚至固态照明。此外，拟议的活动将通过国际合作加强研究基础设施。（来自比利时蒙斯大学的D. Beljonne，荷兰埃因霍温大学的S. Meskers，蒙特利尔大学的C. Silva）摘要：本基金将支持电活性聚合物薄膜性质的理论研究。这些材料作为电子设备的组件（“电子塑料”）具有潜在的应用。然而，要了解它们的基本行为还有很多工作要做。这里提出的工作包括与其他研究这些问题的人进行国际合作，并为从事这个项目的学生和博士后提供了很好的学习机会。

Thin films of pi-conjugated polymers and their oligomer progeny continue to receivewidespread attention as the active materials for organic-based field effect transistors, lightemitting diodes (OLEDs) and solar cells. Despite the many experiments designed to reveal the mechanism(s) by which oligomer/polymer films interact with light, a fundamental appreciation of the relationship between solid-state morphology and photophysical behavior is lacking. In this renewal proposal a strategy is outlined for theoretically investigating an emerging class of supramolecular assemblies based on oligo-p-phenylenevinylene (OPVn) and oligo-thiophene (OTn) derivitives. Side- and end-group functionalization induces chirality and hydrogen bonding in self-assembled nanostructures including helical rod aggregates, rosette shaped aggregates and two-dimensional lamellae. Many of these structures employ p-stacking motifs whichcomplement the more common herringbone packing found in crystals and thin films of the unsubstituted OPVn and OTn molecules. Specific goals include: A detailed understanding of the impact of exciton delocalization, exciton-phonon coupling and disorder on the photo-excited and photo-emissive states in chiral aggregates. Abundant spectral data for helical rod aggregates including steady-state absorption, photoluminescence, circular dichroism (CD) and circularly polarized luminescence (CPL), allows rigorous testing of theoretical models featuring various scenarios for static disorder. A global account for the unusual demise of the CPL dissymmetry magnitude with increasing wavelength observed in OPVn-based helical rod aggregates as well as chiral polythiophene thin films is sought.A robust theoretical account of the deleterious effect of increasing oligomer length on theexciton bandwidth observed in a series of ethylene oxide end-capped OTn fibrillar aggregates (with n=5,6,7). How the bandwidth behaves into the polymer limit is crucial in understanding energy transport and optical properties in thin films of the technologically important regioregular poly(3-alkylthiophenes).Accurate modeling of rapid picosecond energy transport in helical rod aggregates as well as the temporal evolution of the emission spectral line shape following excitation abovethe optical gap. The emission spectral line shape provides valuable information about high energy emissive states. The analysis will be based on the Holstein Hamiltonian, treating excitonic interactions, linear exciton-vibrational coupling, and the influence of point and structural defects on equal footing. The two-particle approximation will be employed to reduce the basis set to a tractable size for numerical analysis without sacrificing accuracy. Excitonic polarons and their steady-state spectral signatures will be evaluated using standard numerical matrix techniques. A Pauli Master Equation will be employed for the exciton transport studies.The broader impact of the proposed activities will be felt primarily through an enhancedunderstanding of a technologically important class of materials, possibly resulting in novel design strategies for improved OLEDs and organic-based solar cells. 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 even solid-state lighting. In addition, the proposed activities will enhance research infrastructure through international collaborations. (D. Beljonne at the Universite de Mons, Belgium; S. Meskers at Eindoven University, The Netherlands; and C. Silva at the University of Montreal.)Non-Technical Abstract: This grant will support theoretical research on the properties of thin films of electrically active polymers. These materials have potential applications as components of electronic devices ("electronic plastics"). However, much needs to be done to understand their fundamental behavior. The work proposed here involves international collaborations with others working on these problems and provides wonderful learning opportunities for students and postdoctoral associates working on this project.