Investigation of the ultrafast dynamics occurring during unsensitized photocatalytic H2 evolution by an [FeFe]-hydrogenase subsite analogue

Pim W. J. M. Frederix, Katrin Adamczyk, Joseph A. Wright, Tell Tuttle, Rein V. Ulijn, Christopher J. Pickett, Neil T. Hunt

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Abstract

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.
Original languageEnglish
Pages (from-to)5888–5896
Number of pages9
JournalOrganometallics
Volume33
Issue number20
Early online date24 Jul 2014
DOIs
Publication statusPublished - 27 Oct 2014

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Hydrogenase
Photochemical reactions
Hydrogen production
Hydrogen
hydrogen production
analogs
photochemical reactions
Molecules
Photosensitizing Agents
Biomimetics
Electronic states
Carbon Monoxide
clean energy
Ground state
Density functional theory
Gases
biomimetics
Spectroscopy
hydrogen
molecular relaxation

Keywords

  • ultrafast dynamics
  • photochemistry
  • spectroscopic measurements

Cite this

Frederix, Pim W. J. M. ; Adamczyk, Katrin ; Wright, Joseph A. ; Tuttle, Tell ; Ulijn, Rein V. ; Pickett, Christopher J. ; Hunt, Neil T. / Investigation of the ultrafast dynamics occurring during unsensitized photocatalytic H2 evolution by an [FeFe]-hydrogenase subsite analogue. In: Organometallics. 2014 ; Vol. 33, No. 20. pp. 5888–5896.
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Investigation of the ultrafast dynamics occurring during unsensitized photocatalytic H2 evolution by an [FeFe]-hydrogenase subsite analogue. / Frederix, Pim W. J. M.; Adamczyk, Katrin; Wright, Joseph A.; Tuttle, Tell; Ulijn, Rein V.; Pickett, Christopher J.; Hunt, Neil T.

In: Organometallics, Vol. 33, No. 20, 27.10.2014, p. 5888–5896.

Research output: Contribution to journalArticle

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AB - 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.

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