CAREER: Elucidating the Interplay Between Exciton Dynamics and Symmetry-Breaking Charge Transfer Through Multidimensional Visible and Mid-Infrared Spectroscopies

在化学系化学结构、动力学和机理(CSDM-A)项目的支持下，宾夕法尼亚大学的Jessica Anna博士和她的团队正在研究将阳光转化为能量的一些最早也是最重要的步骤。太阳能转换通常始于两个或更多紧密堆积在一起的相同分子之间的能量或电荷的转移。由于分子的近似性和相同的结构，很难直接观察转化过程的第一阶段。为了更好地了解这些早期事件及其如何影响太阳能转换效率，安娜博士和她的研究团队使用复杂的激光技术来研究代表更复杂系统的分子对。该团队以一种定义明确的方式改变了两个分子的相对距离和方向，使他们能够区分两个分子相互作用方式的细微差异造成的变化。他们所做的尖端测量为帮助设计和开发用于太阳能转换的新材料提供了新的见解，包括人工光合作用复合体、光催化剂和有机光伏材料。该项目还涉及与研究相关的教育和公共推广活动，包括开发新的教学模块，以便融入研究生、本科和大学预科课堂，以及为本科生、大学预科学生和当地高中教师提供研究机会和带薪实习机会。教学模块、研究机会和带薪实习旨在增加学生在科学、技术、工程和数学(STEM)领域的参与，包括代表性不足的群体和第一代大学生。本项目致力于阐明一类新的pi扩展的金属二吡咯配合物中激子动力学和电荷转移之间的相互作用。这些系统有可能形成激子态，经历对称破坏的电荷转移，从而允许系统地研究能量转移过程和电荷转移过程之间的相互作用。Anna博士和她的学生在可见光和中红外光谱区使用泵浦-探测和相干多维光谱来研究不同的联吡咯配合物，并获得了对称性破坏电荷转移过程中涉及的激发态动力学、结构重排和溶剂重组的完整表征。研究小组使用混合光谱方法来探测具有电荷转移特性的电子激发态分子的演化，利用振动模式对局部静电场的敏感性。该团队使用泵浦-探测光谱来表征布居转移，并确定二吡咯配合物中不同激发态之间的分支比。相干多维光谱测量通过缓解光谱拥塞，分辨激发态中的振动模式，以及阐明溶剂化动力学和其他弛豫过程，提供了更详细的动力学信息。全面的光谱方法使我们更深入地了解了分子内结构重排和溶剂化动力学在破坏对称性的电荷转移过程中的组合作用，这对太阳能转换和其他应用非常重要。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Dr. Jessica Anna and her group at the University of Pennsylvania are investigating some of the earliest, and most important steps involved in the conversion of sunlight into energy. Solar energy conversion often begins with the transfer of energy or charge between two or more identical molecules that are packed together tightly. The close proximity and identical structures of the molecules make it very difficult to directly observe the first stages of the conversion process. In order to better understand these early events and how they affect solar energy conversion efficiency, Dr. Anna and her research team use sophisticated laser techniques to study pairs of molecules that represent more complicated systems. The team varies the relative distance and orientation of the two molecules in a well-defined way that allows them to distinguish changes caused by subtle differences in the way the two molecules interact with each other. The cutting-edge measurements they make provide new insight to aid in the design and development of new materials for solar energy conversion, including artificial photosynthetic complexes, photocatalysts, and organic photovoltaic materials. The project also involves educational and public outreach activities related to the research, including the development of new teaching modules for integration into graduate, undergraduate, and pre-college classrooms, as well as research opportunities and paid internships for undergraduates, pre-college students, and local area high school teachers. The teaching modules, research opportunities, and paid internships are designed to increase the participation of students in science, technology, engineering, and mathematics (STEM) fields, including underrepresented groups and first-generation college students. This project focuses on elucidating the interplay between exciton dynamics and charge transfer in a new family of pi-extended metallo-dipyrrin complexes. These systems have the potential to form excitonic states that undergo symmetry-breaking charge transfer, and therefore allow a systematic investigation of the interplay between energy- and charge-transfer processes. Dr. Anna and her students use pump-probe and coherent multidimensional spectroscopy in the visible and mid-IR spectral regions to study the different dipyrrin complexes and obtain a full characterization of the excited-state dynamics, structural rearrangement, and solvent reorganization involved in the symmetry-breaking charge transfer process. The research team uses a mixed spectral approach to probe the evolution of molecules in electronically excited states having charge-transfer character, harnessing the sensitivity of vibrational modes to the local electrostatic field. The team uses pump-probe spectroscopy to characterize population transfer and determine the branching ratios among different excited states in the dipyrrin complexes. The coherent multidimensional spectroscopy measurements provide more detailed information on the dynamics by alleviating spectral congestion, resolving vibrational modes in the excited state, and elucidating solvation dynamics and other relaxation processes. The comprehensive spectroscopic approach yields a deeper understanding of the combined role of intramolecular structural rearrangement and solvation dynamics in symmetry-breaking charge transfer processes that are important for solar energy conversion and other applications.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.