Excitonic Coupling in Molecular and Polymeric Aggregates: Beyond Conventional J- and H-aggregation

有机分子和聚合物作为半导体材料在广泛的实际应用中继续受到关注，包括纸质电子、固态照明、太阳能电池和组织生长支架。大多数设备都受益于快速能量传输，这取决于一个分子上的电子激发能以多快的速度转移到更远的分子。然而，尽管经过了50多年的深入实验和理论研究，关于有机分子聚集体、薄膜和晶体中电子激发的性质仍然存在许多问题。提出的研究的主要目的是发展一种考虑到分子相对组织的分子间电子耦合理论。这一理论将提供有关能量转移速率的信息，并将揭示有关电子激发特性的重要信息，这些信息可用于设计更高效的设备。PI的团队还将探索使用光学微腔来控制材料特性。微腔由两个镜子组成，它们之间的距离非常短，大约为百万分之一米。在这种镜子之间插入材料，光和物质之间的相互作用被大大放大。拟议的研究将受益于与马萨诸塞大学和蒙特利尔大学实验组的合作。拟议研究的更广泛影响将是加强对技术上重要的一类材料的光物理和输运特性的理解。有机电子设备的商业影响预计将在未来十年大幅增加，如柔性显示器、电子标签、固态照明和太阳能电池等产品。本文研究的分子聚集体提供的广泛的光物理和传输行为可以为高效太阳能吸收剂和发光材料的新设计范例提供基础。本研究的主要目标是建立一种分子聚集体的光物理响应理论，该理论解释了组成分子之间同时存在的远程库仑相互作用和短程电荷转移（CT）相互作用。该理论将考虑电子耦合、电子-核耦合以及对角线和非对角线无序的平等基础，并将Kasha的传统J-和h -聚集模型扩展到分子pi堆栈等系统，在这些系统中，相邻分子之间的非常接近允许分子轨道之间的显著重叠。研究计划了解不同聚集体类型的光物理和输运性质，以及当绝热CT激子从母体Frenkel激子调谐时，这些聚集体如何演变成传统的H-和j -聚集体。还将进行研究，以确定聚集体的性质如何改变浸泡在调谐光学微腔。分析将基于一粒子和二粒子基集表示的类荷尔斯泰因哈密顿量。基本激励和他们的频谱特征将评估使用数值矩阵技术。将具体应用于作为染料颜料和电子传输材料的苯乙烯pi-堆，以及在光伏器件中作为优异激子传输材料的聚（3-己基噻吩）pi-堆。拟议的研究将受益于与马萨诸塞大学和蒙特利尔大学实验组的合作。拟议研究的更广泛影响将是加强对技术上重要的一类材料的光物理和输运特性的理解。有机电子设备的商业影响预计将在未来十年大幅增加，如柔性显示器、电子标签、固态照明和太阳能电池等产品。本文研究的分子聚集体提供的广泛的光物理和传输行为可以为高效太阳能吸收剂和发光材料的新设计范例提供基础。

NONTECHNICAL SUMMARYOrganic molecules and polymers continue to receive attention as semiconducting materials in a wide array of practical applications, including paper electronics, solid-state lighting, solar cells and scaffolds for tissue growth. Most devices benefit from rapid energy transport, which is dictated by how fast an electronic excitation on one molecule can be transferred to a more distant molecule. However, despite the more than five decades of intensive experimental and theoretical research, there are still many questions regarding the nature of the electronic excitations in organic molecular aggregates, thin films and crystals. The main objective of the proposed research is to develop a theory of electronic coupling between molecules which takes into account the organization of molecules relative to each other. This theory will provide information about the rate of energy transfer and will reveal important information about the properties of the electronic excitations, information that can be used to design more efficient devices. The PI's group will also explore the use of optical microcavities for controlling material properties. Microcavities consist of two mirrors separated by a very short distance of the order of one millionth of a meter. The interaction between light and matter is greatly amplified for materials inserted between such mirrors. The proposed research will benefit from collaborations with the experimental groups at the University of Massachusetts and the University of Montreal. The broader impact of the proposed research will be in an enhanced understanding of the photophysical and transport properties of a technologically important class of materials. The commercial impact of organic electronic devices is expected to dramatically increase over the next decade through products like flexible displays, electronic labels, solid-state lighting and solar cells. The wide array of photophysical and transport behaviors afforded by molecular aggregates studied in this proposal could provide the basis for novel design paradigms for efficient solar absorbers and light emitting materials.TECHNICAL SUMMARYThe main goal of the proposed research is to develop a theory for the photophysical response of molecular aggregates which accounts for the simultaneous presence of long-range Coulombic interactions and short-range charge-transfer (CT) interactions between the constituent molecules. The theory will consider the electronic coupling, the electronic-nuclear coupling, and diagonal and off-diagonal disorder on equal footing and will extend the conventional J- and H-aggregate model of Kasha to systems such as molecular pi-stacks, in which the very close proximity between neighboring molecules allows for significant overlap between molecular orbitals. Investigations are planned to understand the photophysical and transport properties of different aggregate types and how such aggregates evolve into conventional H- and J-aggregates as the adiabatic CT exciton is tuned away from the parent Frenkel exciton. Studies will also be undertaken to determine how aggregate properties are altered by immersion into a tuned optical microcavity. The analyses will be based on Holstein-like Hamiltonians represented in a one- and two-particle basis set. Fundamental excitations and their spectral signatures will be evaluated using numerical matrix techniques. Specific applications will be made to rylene pi-stacks which have been studied as dye pigments and electron-transporting materials, as well as poly(3-hexylthiophene) pi-stacks which make excellent exciton transporting materials in photovoltaic devices. The proposed research will benefit from collaborations with the experimental groups at the University of Massachusetts and the University of Montreal. The broader impact of the proposed research will be in an enhanced understanding of the photophysical and transport properties of a technologically important class of materials. The commercial impact of organic electronic devices is expected to dramatically increase over the next decade through products like flexible displays, electronic labels, solid-state lighting and solar cells. The wide array of photophysical and transport behaviors afforded by molecular aggregates studied in this proposal could provide the basis for novel design paradigms for efficient solar absorbers and light emitting materials.