The [Fe-Fe]-hydrogenases are extraordinarily efficient biological catalysts for reducing protons to generate hydrogen gas. The active site of the enzyme contains two central iron atoms with a bridging dithiolate ligand, and multiple CO and CN ligands on the irons. Many small-molecule models of the active site have been developed that contain some or all of the structural features of the [FeFe]-hydrogenase active site. Some of these model compounds also contain a photosensitizer, which could allow the absorption of light to drive the reduction of hydrogen. Understanding the dynamics of the active site of these and related model compounds is important for ultimately designing effective, light-driven catalysts, since the long-lived photochemistry affects the overall catalytic behaviour at the active site. Over the past 15 years, I have worked with 16 undergraduate students studying these compounds using ultrafast UV/visible pump, infrared probe ultrafast time-resolved spectroscopy, in collaboration with the National Institute of Standards and Technology. In this talk, the time-dependent photochemistry of several hydrogenase model compounds is examined. Substantial differences in the photochemical behaviour are found depending on ligand substitution at the model active site. All model compounds studied to date produce CO-loss products when excited with UV and/or visible light, and these product isomers persist for several microseconds and longer. Model compounds with only CO ligands or CO and PMe3 ligands also show excitation of long-lived (150 ps) excited states, either competing with or in addition to CO loss. Models with PMe3 ligands also show isomerization upon CO loss. Interestingly, models with only CO and CN ligands show no evidence of the long-lived excited state and only exhibit CO loss and isomerization. Substitution of two CO ligands with bipyridine and 1,10-phenylanthracene exhibit partial short-lived isomerization and only small amounts of long-lived CO-loss products.

Time-resolved infrared spectroscopy of [FeFe]-hydogenase model compounds:  15 years of ultrafast laser experiments with undergraduates

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.