The Exchange Mechanism and Exciton Migration in Organic Semiconductors

摘要：有机半导体仍然是下一代光学和电子材料广泛应用的焦点。与硅等无机半导体相比，有机半导体的分子多样性，由于合成有机化学，提供了几乎无限的潜力。当与材料科学相结合时，这种丰富的分子挂毯表明了对光学和机械性能、材料成本、环境影响和设备结构简单性的非凡控制。固体状态下能量的有效转移是发光和光收集装置的基本方面之一。更好地理解分子设计与有机材料中能量转移之间的关系，可以设计出更高效的下一代光学和电子设备。这项研究的目标是一种历史上很少受到关注的能量转移机制，一种被称为交换的机制。这种机制在所有分子系统中都是有效的，更好地理解它是如何在固态中促进能量转移的，将为更广泛的新型、更高效的有机电子学打开大门。该项目包括向数千名来自弱势社会经济背景的三年级至六年级学生介绍能源的基本概念，以及在STEM领域接受大学教育的基本理念。技术摘要：激子输运的第一步是发色团间的能量转移。从历史上看，简单性促进了具有感应转移机制的发射材料和具有交换机制的非发射材料的二元关联。这种区别并不总是与观察相一致。这项研究使人们对每种机制的作用有了更好的了解。实验的可及性已经把注意力集中在发光系统上。认识到器件固有的高分子密度有助于交换，并认识到交换不具有与感应相同的限制，这项工作填补了对非发光材料输运理解的空白。同时，这项工作正在阐明这两种机制的联合作用。利用发光和非发光材料中激子扩散的方法，这项工作阐明了利用联合方法进行输运的方法，通过湮灭和极化子捕获量化寄生激子猝灭，并测量激子裂变对能量输运的影响。总的来说，这项研究为理解有机半导体中的激子输运和开发设计原则提供了重要贡献，以增强下一代光收集和发光器件。该项目同时培养多名研究生在广泛的最先进的物理和材料科学理论和实验技术。

Nontechnical Abstract:Organic semiconductors remain the focus of a broad range of next generation optical and electronic materials applications. Compared with inorganic semiconductors such as silicon, the molecular variety available for organic semiconductors, thanks to synthetic organic chemistry, offers near limitless potential. When combined with materials science, this rich molecular tapestry suggests availability of extraordinary control over optical and mechanical properties, materials cost, environmental impact, and simplicity of device construction. Efficient transfer of energy in the solid state is one of the fundamental aspects of both light-emitting and light harvesting devices. A better understanding of the relationship between molecular design and the transfer of energy in organic materials enables design of a broad range of more efficient next-generation optical and electronic devices. This research targets one of the energy transfer mechanisms that historically received less attention, a mechanism known as exchange. This mechanism is operative in all molecular systems, and a better understanding of how it contributes to energy transfer in the solid state will open the door to a broad range of new, and more efficient organic electronics. This project includes introducing thousands of third through sixth grade students from disadvantaged socioeconomic backgrounds to the fundamental concept of energy and the basic idea of pursuing a college education in a STEM field.Technical Abstract:The first step in exciton transport is inter-chromophore energy transfer. Historically, simplicity has promoted binary association of emissive materials with an inductive transfer mechanism and non-emissive materials with an exchange mechanism. This distinction has not always been consistent with observation. This research is developing a better understanding of the role of each mechanism. Experimental accessibility has focused previous attention on luminescent systems. Realizing that the high molecular density inherent to devices facilitates exchange, and acknowledging that exchange does not have the same limitations as induction, this work is filling gaps in the understanding of transport in non-luminescent materials. At the same time, this work is elucidating the combined roles of both mechanisms. Employing methodologies to probe exciton diffusion in both luminescent and non-luminescent materials, this work is elucidating ways to exploit combined approaches to transport, quantifying parasitic exciton quenching via annihilation and polaron trapping, and measuring the effects of exciton fission on energy transport. Taken in aggregate, this research is providing a significant contribution to the understanding of exciton transport in organic semiconductors and developing design principles to enhance the next generation of light harvesting and light-emitting devices. The project is simultaneously training multiple graduate students in a wide range of state-of-the-art physical and materials science theory and experimental techniques.