NSF Award
2437814
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. <br/><br/>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.<br/><br/>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.
