Ultrafast dynamics of [NiFe] hydrogenase models

The [NiFe] hydrogenase mimic [Ni(dppe)(pdt)Fe(CO)3] ([NiFe-1]) was one of the first to be capable of catalyzing dihydrogen generation. When [NiFe-1] is converted to [Ni(dppe)(pdt)-µH-Fe(CO)3]+ ([NiFeH]), in which a hydride group bridges the Ni-Fe bond, the geometry at the Ni center changes from tetrahedral to square planar.1 Some of the proposed short lived intermediates in the catalytic cycle, such as the Ni(II)Fe(0) pseudo- square planar state, have not been isolated or observed. [NiFe-1] was examined with ultrafast transient spectroscopy to learn more about its geometry change and the resulting effect on its electron transfer mechanism. Visible pump techniques were used to probe changes in the excited state of [NiFe-1] in response to light, by tracking changes in the IR and UV-visible absorption spectra. [NiFe-1] relaxes through its singlet manifold to the lowest energy singlet excited state within the time resolution of the instrument (<100 fs). Intersystem crossing to the triplet excited state occurrs in 7 ps, and it relaxes back to the ground state within 40 ps. [NiFe-1] relaxes faster than the [FeFe] mimics2–6 due to its lower lying triplet state (~ 1.6 eV lower than [FeFe(pdt)(CO)6]). [NiFe-1] also undergoes photolytic CO-loss and the product is stabilized by coordination of a THF solvent molecule. The chromophore perylene diimide (PDI) was tethered to [NiFe-1] through a phosphine linker group coordinated to the iron center. Excitation of the PDI at 530 nm resulted in a charge transfer from the [NiFe] center, observable in the transient UV-vis spectrum. The charge transfer state formed within a lifetime of 2 ps, and disappeared through charge recombination occurring in around 40 ps. A long-lived 5.7 ns absorption observed during these measurements could be a long lived *PDI based excited state, a CO loss product, or potentially a longer lived charge transfer state. Further studies with more metal centered techniques are needed elucidate the identity of the long-lived state.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Boedicker, Lauren

Contributors dc:contributor

• Vura-Weis, Joshua
• Mirica, Liviu M
• Olshanksy, Lisa
• Girolami, Gregory S

• [NiFe] Hydrogenase Mimics
• Ultrafast Dynamics
• Transient Spectroscopy
• Donor-Acceptor
• Charge Transfer

Statement dc:rights

• Copyright 2025 Lauren Boedicker

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129594

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129594