(Invited) Excited States and Reaction Mechanisms of Catalysts with Redox Active Ligands Investigated with X-Ray Spectroscopy

Abstract

Metal dithiolenes and related molecular catalysts known for their redox-active ligands and their efficient and robust electro- and photo-catalysis of the hydrogen evolution reaction are investigated. To understand how the redox-active ligands of these catalysts influence their electronic excited states and participate in their chemical reactions, we need element-specific probes of charge and bonding at both metal and ligand atomic sites. X-ray absorption spectroscopy (XAS) affords us this opportunity and is used to study the electro- and photo-catalytic reaction mechanisms of these complexes, with a specific focus on the role of metal versus ligand atomic sites. Steady-state and time-resolved XAS studies at the Ni and S K-edges will be presented to identify the redox activity of metal vs. ligand sites on timescales spanning from the ultrafast excited state relaxation and photochemical activation processes to the steady-state creation of important intermediates in the multi-step hydrogen evolution reaction.