Research students are dialing in on the proton: Understanding the role of the proton in photo-induced, proton-coupled electron transfer using tunable model systems.
Professor Elizabeth R. Young’s lab is studying electron transfer in model molecular systems. These models are inspired by biological systems, specifically proteins, which carry out reactions necessary for life very efficiently. Results of this research could lead to the development of more energy efficient reactions, including splitting water into hydrogen and oxygen for energy storage, nitrogen fixation for agriculture and carbon dioxide reduction to decrease greenhouse gases in the atmosphere. Additionally, this project enhances the research infrastructure in the Pioneer Valley of Massachusetts.
Proton-coupled electron transfer (PCET) drives numerous critical reactions in natural systems, including the light-harvesting reactions of photosynthesis. This project explores several features in the mechanistic study of PCET. The interplay between electron transfer driving force and the proton transfer ability of acid groups in a series of donor and acceptor systems will be studied in order to provide direct insight into how hydrogen-bonded interfaces modulate electron transfer. Specific questions to be answered include: For which electron transfer driving force ranges does the proton transfer ability make a substantial difference in the observed rates? Does the ability of a proton within the interface result in significant modulation in the electron transfer rate between the same donor and acceptor moieties? Does the mode of supramolecular donor-acceptor assembly have a significant impact on coupling and electron transfer rates? These mechanistic studies of PCET provide important insights into how light could be used to initiate chemical reactions that are facilitated by the concerted movement of protons and electrons.
Schematic representation of a bimolecular PCET model system. Ferrocene-amidinium serves as the electron and proton donor. The protonation state of amidinium acidic functionality gates the elecron transfer rate between ferrocene-amidinium and the Ru(II)(2,2’-bipyridine)3 photooxidant.
Hydrogen bonded D-A system in which a carboxylate-appended moiety binds axially to the phlorin scaffold. Electron transfer is mediated by the hydrogen bonded interface.