Resolving the Fates of Multiple Triplet Excitons in Single Multi-Chromophoric Conjugated Organic molecules

有机聚合物是由重复的分子亚基组成的长链。当它们吸收光时，链的某些部分处于激发态，这种激发态可以存活十亿分之一秒。然而，这些能量的一小部分会被困在较低的能量状态中，这种状态持续的时间要长得多，也许要长一千倍。这些较长寿命的状态可以相互作用，以及存在于链上的多余电荷，这对在新兴技术中使用聚合物提出了重大挑战，例如发光二极管和太阳能转换设备。在化学系大分子、超分子和纳米化学项目的支持下，新墨西哥大学的约翰·格雷教授正在广泛的时间尺度上研究这些长寿状态。格雷教授和他的学生一起使用显微镜方法观察单个聚合物链，以确定链结构和填料如何影响这些长时间的激发。他们的发现可以为新聚合物的设计提供信息。此外，格雷教授本人也是一名退伍军人，他正在与新墨西哥大学的退伍军人学生团体合作，通过每周的“午餐学习”和辅导课程，提高退伍军人和非传统学生在STEM领域的参与度。长期目标是通过认识到退伍学生的独特经历，并让他们成为课堂和实验室环境中的领导者，来提高他们的入学率和保留率。该项目研究了多色共轭聚合物和分子光收集阵列中自旋禁止（三重态）激发态的居群动力学。混合单分子光谱技术和随机动力学建模是主要的物理探针，用于解决从大约1ns到稳态条件的时间尺度上的多个三重体之间的相互作用。目标是能够在任何给定时间内计算单个分子上的三重态的数量，并解决这些状态及其与其他激发态的相互作用如何随着结构（形态）复杂性的增加而演变。该项目还揭示了双分子湮灭过程的新动力学见解，这些过程通常难以在大块材料水平上可靠地测量。该研究进一步利用与合成材料化学家的合作来研究分子结构的微调如何影响多个相互作用激发态的种群动力学。学生参与者将获得物理和材料化学方面的宝贵技能，以及对国家科学技术利益发展至关重要的理论建模。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Organic polymers are long chains of repeating molecular subunits. When they absorb light, some segments of the chain are placed in excited energy states that live for about a billionth of a second. However, a fraction of this energy can become trapped in lower energy states that last much longer, perhaps a thousand times longer. These longer-lived states can interact with each other, as well as excess charges existing on the chain, which poses significant challenges for using polymers in emerging technologies, such as light-emitting diodes and solar energy conversion devices. With support from the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor John Grey at University of New Mexico is studying these long-lived states over a broad range of time scales. Working with his students, Professor Grey is using microscopy methods that can observe single polymer chains to determine how the chain structure and packing influence these long-lived excitations. Their discoveries could inform the design of new polymers. In addition, Professor Grey, who is a veteran himself, is engaging with student veteran groups at the University of New Mexico to increase participation of veteran and non-traditional students in STEM fields though weekly 'lunch and learn' and tutoring sessions. The long-term goal is to improve enrollment and retention of student veterans by recognizing their unique experience and engaging them as leaders in classroom and laboratory settings.The project examines the population dynamics of spin-forbidden (triplet) excited states in multi-chromophoric conjugated polymers and molecular light harvesting arrays. Hybrid single molecule spectroscopy techniques and stochastic kinetic modeling are the primary physical probes used to resolve interactions between multiple triplets spanning time scales from approximately 1 ns up to steady-state conditions. The goal is to be able to count the number of triplets on a single molecule at any given time, and to resolve how these states and their interactions with other excited states evolve with increasing structural (morphological) complexity. This project also exposes new kinetic insights of bimolecular annihilation processes that are often difficult to measure reliably at the bulk material level. The research further utilizes collaborations with synthetic materials chemists to investigate how fine tuning of molecular structure impacts population dynamics of multiple interacting excited states. Student participants gain valuable skills in physical and materials chemistry as well as theoretical modeling vital for the advancement of National science and technology interests.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.