Photochemical Dynamics of a Trimethyl-Phosphine Derivatized [FeFe]-Hydrogenase Model Compound
Edwin J. Heilweil, Rachel L. Meyer, Tara M. Biser, Anet D. Zhandosova, Christopher J. Stromberg
Coupling photosensitizers with [FeFe]-hydrogenase model compounds can potentially create light- driven catalysts for production of hydrogen gas from acidic protons. Though there have been many studies on the synthesis, kinetics, and reaction mechanisms of these photosensitizer-model complexes, few have looked at how the [FeFe]-hydrogenase models react upon exposure to light. To extract detailed photoreaction information, ultrafast time-resolved UV or visible pump IR probe spectroscopy (TRIR) was performed on Fe2(μ-S2C2H4)(CO)4(PMe3)2 (2b) dissolved in room temperature heptane and acetonitrile and the photochemical dynamics were determined. Excitation with 532 nm and 355 nm light produces bleaches and new absorptions that decay to half their original intensity with times constants of 390 ± 120 ps in heptane and 300 ± 120 ps in acetonitrile, respectively. These spectral features persist to at least the microsecond timescale. The photochemical dynamics of 2b is assigned to formation of an initial set of photoproducts, which were a mixture excited-state tricarbonyl (3-CO) isomers. These isomers further decay into another set of long-lived photoproducts in which approximately half of the excited-state 3-CO isomers recombine with CO to form another complex mixture of 3-CO and tetracarbonyl (4-CO) isomers.