Singlet fission and exciton diffusion in organic molecular crystal materials

加州大学河滨分校的克里斯托弗·巴特尔斯得到化学系化学结构、动力学和机制项目的支持，开展研究，探索激子结构如何影响分子晶体系统中的激发态动力学，重点是与有机光伏材料相关的过程。该研究计划旨在实现三个目标。首先，该团队将继续他们的合作工作，使用时间分辨发光光谱和理论来表征聚并苯分子晶体中的离域激子态。其次，将研究单重态裂变的动力学和反应机制，单重态裂变是一个吸收单个光子导致产生两个激子和潜在的两个电子-空穴对的过程。 结晶并四苯将成为阐明这种独特的弛豫过程如何工作的模型系统。 第三，有机系统中的能量迁移，这在确定太阳能电池的效率发挥了重要作用，将使用光学瞬态光栅实验的修改版本进行研究。 目标将是通过使用驻波和高动态范围检测的组合来测量20 nm或更小的激子扩散长度。 这项研究的总体目标是对激子特性（如离域）如何影响单线态裂变和激子扩散产生基本见解，从而提供一种评估晶体有机材料在光伏应用中的最终潜力的方法。 这种理解反过来可以帮助设计改进的太阳能电池材料，并解决一个重要的社会问题：对清洁，廉价和可再生能源的需求。研究生和博士后将在技术关键领域接受培训。还将向招收科学专业代表性不足群体的大部分学生的当地小学开展外联活动。

Christopher Bardeen of the University of California-Riverside is supported by the Chemical Structure, Dynamics and Mechanisms Program in the Division of Chemistry to carry out research to probe how exciton structure impacts excited state dynamics in molecular crystal systems, with an emphasis on processes relevant for organic photovoltaic materials. The research plan is designed to accomplish three objectives. First, the team will continue their collaborative work on using time-resolved luminescence spectroscopy and theory to characterize delocalized exciton states in polyacene molecular crystals. Second, the dynamics and reaction mechanism of singlet fission, a process whereby a absorption of a single photon leads to the creation of two excitons, and potentially two electron-hole pairs, will be studied. Crystalline tetracene will be a model system for clarifying how this unique relaxation process works. Third, energy migration in organic systems, which plays an important role in determining solar cell efficiencies, will be studied using a modified version of the optical transient grating experiment. The goal will be to measure exciton diffusion lengths of 20 nm or less by using a combination of standing waves and high dynamic range detection. The overall thrust of this research is to generate fundamental insights into how exciton properties like delocalization can affect singlet fission and exciton diffusion, thus providing a way to assess the ultimate potential of crystalline organic materials for photovoltaic applications. This understanding in turn could aid in the design of improved materials for solar cells and address an important societal problem: the need for clean, inexpensive, and renewable energy. Graduate students and postdoctoral associates will be trained in technologically vital areas. Outreach activities to local elementary schools which enroll a majority population of students from underrepresented groups in science will also be initiated.