Mechanisms of Proton Coupled Electron Transfer

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Dr. Thomas J. Meyer, Chemistry Department, University of North Carolina - Chapel Hill, is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program of the Chemistry Division for studies of the mechanism of proton coupled electron transfer (PCET) reactions. Specifically, this study will target a particular type of PCET reactions, Electron Proton Transfer (EPT) in which concerted electron-proton transfer occurs from orbitally separated sites on the donor to orbitally separated sites on an acceptor or acceptors. Although more complex than electron transfer followed by proton transfer or vice versa, EPT can dominate PCET reactivity by avoiding high energy intermediates. Light-driven or optical EPT will be investigated for charge transfer within molecules, within H-bonded association complexes, and in ligand-bridged mixed valence complexes. This work will utilize a combination of spectroscopic and dynamic measurements to characterize optical EPT, including ultrafast measurements. The goal is to demonstrate the breadth of optical EPT phenomena and to use spectroscopic and dynamic information combined with theory to gain insight about EPT at a level comparable to our current understanding of electron transfer. Additionally, a new type of metal complex excited state reactivity based on EPT quenching with coupled proton transfer will be explored. EPT quenching and back reactions will be investigated using transient absorption, emission, and infrared techniques to follow the exchanging proton and to establish kH/kD kinetic isotope effects and free energy dependences in the normal and inverted regions.Most important energy related and/or biologically relevant reactions for energy conversion involve catalyzed multi electron, multi proton changes. For example, in biological reactions, catalyst activation typically occurs one electron at a time at spatially separated sites. This project will examine the detailed mechanism of how electrons and protons are transferred in such processes and, thus, will shed light on how important electron transfer reactions actually occur. In addition to the scientific contributions, this project will provide a cross over between synthesis and measurements with application of theory creating an excellent environment for engaging and training undergraduates and graduate students, and postdoctoral research fellows.