CAREER: Mapping the Mechanisms of Photoredox Catalysis with Multidimensional Optical Spectroscopy

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Vanessa Huxter of the University of Arizona is using advanced spectroscopic methods to study the initial steps of light-driven catalytic reactions that generate both simple and complex molecules under mild conditions. To understand how these reactions work, Dr. Huxter and her students will use pulses of light as short as a millionth of a billionth of a second (one femtosecond), to track the chemical species produced by light-triggered chemical reactions over a wide range of times. The project will address the knowledge gap between the short lifetimes of intermediate radical species that are implicated in driving such reactions, and the longer timescales of diffusion required for those reaction to happen. Their discoveries could lead to a better understanding of catalysts used in the synthesis of industrially and pharmaceutically important chemicals that are otherwise difficult to produce. In addition, graduate students working on this project will receive advanced training in multiple disciplines, including optics, chemistry, and physics, and the project will engage students of underserved communities through the development and deployment of 3D-printed spectrometers that will bring hands-on learning to students from historically underrepresented groups. The Huxter group uses time-resolved fluorescence, ultrafast broadband transient absorption, and two-dimensional electronic spectroscopy across a wide range of time and energy scales to study photoinduced single-electron transfer in photoredox catalytic systems. The initial steps of organic photoredox catalytic processes will be tracked to reveal the free energy landscapes associated with such reaction mechanisms. This research will identify the driving forces and intermediate states for photoredox catalytic reactions, which could open pathways to design new, efficient catalysts. This work could contribute to the resolution of a controversy regarding the mismatch between the short lifetimes of radical intermediates and the requirement for diffusion-limited bimolecular interactions. The role of radicals as intermediates in photoredox catalysis will be further studied using isolatable neutral radicals. In addition, the Huxter group will investigate the influence vibrational modes on photocatalytic charge transfer events. 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.