CAS: Exploring Multiexciton Dynamics for Triplet Upconversion in Structurally Well-Defined Covalent Dimers

在这个由美国国家科学基金会化学部化学结构、动力学和机理B项目资助的项目中，科罗拉多大学博尔德分校化学系的Niels Damrauer和Tarek Sammakia正在努力对一个被称为“三重态上转换”（TUC）的过程有更深入的了解。当分子吸收光时，它们被激发成一个更高的能量状态，在TUC中，两个激发态分子的能量融合成一个更有能量和更大的反应电位的单一激发态。TUC光物理学是强大的，适用于广泛的化学、技术和生物应用，包括太阳能转换、化学催化、光促进聚合和生物成像。这个项目将光谱学、化学合成和理论结合起来，考虑这一过程的基本方面。在这项研究中获得的理解将推动下一代分子和材料在操纵通过吸收获得的光能方面达到新的水平。研究小组还将通过与丹佛大都会地区的DSST学校建立关系，在高中层面进行科学推广。这是一个了不起的以stem为基础的学校系统，在总人口中，71%的人经济困难，绝大多数人种族多样化，高中毕业生的大学录取率为100%。为了应对COVID危机，该团队通过在线同步平台提供了为期8周的选修课，使用高度可访问的3d打印部件、其他一些廉价组件和手机摄像头探索光谱学和光物理学。本项目围绕激发态动态控制的思想展开。在绝大多数TUC系统中，使用单体发色团，并要求碰撞或非扩散单体/单体相遇来协商所有三重态聚变事件。这导致对多激子动力学的控制很少，而多激子动力学是影响总产率的关键因素。由于自旋统计在起作用，并且由于TUC所需的单线态通道在其统计权重上是最小的，因此问题受到挑战。在这个项目中，该团队计划从根本上改变和询问多激子途径的数量和类型，这些途径可能有助于使用结构明确的二聚体系统成功实现TUC。该团队认为，他们的系统的结构定义与他们对物理化学性质的控制相一致，如激发态反应驱动力、激发态耦合、发色团间自旋耦合的大小、分子大小和溶解度，将有可能使他们能够评估利用分子内多激子动力学获得的TUC效率增益。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。

In this project, funded by the Chemical Structure, Dynamics & Mechanism B Program of the NSF Division of Chemistry, Niels Damrauer and Tarek Sammakia of the Department of Chemistry at the University of Colorado Boulder are working to gain a greater understanding of a process called “triplet upconversion” (TUC). When molecules absorb light, they are excited into a higher energy state and in TUC, the energy of two excited molecules fuses into a single excited state that is more energetic and has greater reactive potential. TUC photophysics is robust and applicable to a remarkable breadth of chemical, technological, and biological applications including solar energy conversion, chemical catalysis, light-promoted polymerization, and biological imaging. This project marshals a program that joins spectroscopy, chemical synthesis, and theory to consider fundamental aspects of this process. The understanding gained in this research will push the next-generation of molecules and materials to new levels in their ability to manipulate light energy obtained through absorption. The research team will also engage in scientific outreach at the high school level through an established relationship with the DSST schools in the Denver metropolitan area. This is a remarkable STEM-based school system with a 100% college acceptance rate for high school graduates amongst a total population that is 71% economically challenged and overwhelmingly racially diverse. Through an online synchronous platform in response to the COVID crisis, the team offer an 8-week elective to explore spectroscopy and photophysics using highly accessible 3D-printed parts, a few other inexpensive components, and a cell phone camera. This project centers around the ideas of excited state dynamical control. In the vast majority of TUC systems, monomer chromophores are used, and collisions or non-diffusional monomer/monomer encounters are called upon to negotiate all triplet fusion events. This results in very little control of the multiexciton dynamics that are critical contributors to overall yield. Matters are challenged because spin statistics are in play and because the singlet channel required for TUC is the smallest in its statistical weight. In this project, the team plans to fundamentally alter, and interrogate, the number and types of multi-exciton pathways that may contribute to successful TUC using structurally well-defined dimer systems. The team believes that the structural definition of their systems in concert with the control they maintain in manipulating physiochemical properties – such as excited state reaction driving force, excited state couplings, interchromophore spin coupling magnitudes, molecular size, and solubility – will potentially allow them to assess TUC efficiency gains achieved by exploiting intramolecular multiexciton dynamics.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.