Electron transfer and proton transfer reactions are the core of light-driven catalytic reactions such as those that result in water oxidation, carbon dioxide reduction, and hydrogen evolution. Proton-coupled electron transfer (PCET) reactions tether the two events together allowing for redox-leveling of multi-electron processes. As nature demonstrates in photosystem II, PCET reactions can provide redox pathways that posit lower activation barriers for the reactions to occur versus step-wise redox and proton transfer reactions. This decrease in the activation barrier is a result of bypassing high-energy intermediates that would normally form following the stepwise reaction pathway. Of recent interest in the field of PCET are reactions evolving from the excited state of a particular chromophore. Presented herein are some preliminary experiments demonstrating the ability for ruthenium(II) heteroleptic complexes employing hydroxylated polypyridyl ligands to effectively engage in excited state PCET reactions with a series of 4,4’-bipyridinium proton/electron acceptors. The reactions presented here are thermodynamically unfavorable from the ground state of these complexes. Key to understanding these ruthenium(II) systems involves primary investigation of excited state proton transfer and electron transfer reactions. Among the information presented here will be an overview of the free energy dependence for proton transfer reactions from the excited state of the Ru(II) complexes to a series of pyridine derivatives.

Proton transfer and proton-coupled electron transfer reactions of heteroleptic ruthenium(II) complexes incorporating hydroxylated polypyridyl ligands

255th National Meeting (2018)

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