Biomimetic compounds based upon the active subsite of the [FeFe]-hydrogenase enzyme system have been the focus of much attention as catalysts for hydrogen production: a clean energy vector. Until recently, use of hydrogenase subsite systems for light-driven hydrogen production has typically required the involvement of a photosensitizer, but the molecule [(μ-pdt)(μ-H)Fe2(CO)4(dppv)]+, (1; dppv = cis-1,2-C2H2(PPh2)2; pdt = 1,3-propanedithiolate) has been reported to catalyze the evolution of hydrogen gas under sensitizer-free conditions. Establishing the molecular mechanism that leads to photohydrogen production by 1 is thus an important step that may enable further development of this family of molecules as solar fuel platforms. Here, we report ultrafast UVpump–IRprobe spectroscopy of 1 at three different excitation wavelengths and in a range of solvents, including under the conditions required for H2 production. Combining spectroscopic measurements of the photochemistry and vibrational relaxation dynamics of 1 with ground-state density functional theory (DFT) calculations shows that, irrespective of experimental conditions, near-instantaneous carbonyl ligand loss is the main photochemical channel. No evidence for a long-lived excited electronic state was found. These results provide the first time-resolved data for the photochemistry of 1 and offer an alternative interpretation of the underlying mechanism of light-driven hydrogen generation.
- ultrafast dynamics
- spectroscopic measurements
Frederix, P. W. J. M., Adamczyk, K., Wright, J. A., Tuttle, T., Ulijn, R. V., Pickett, C. J., & Hunt, N. T. (2014). Investigation of the ultrafast dynamics occurring during unsensitized photocatalytic H2 evolution by an [FeFe]-hydrogenase subsite analogue. Organometallics, 33(20), 5888–5896. https://doi.org/10.1021/om500521w