Dye-sensitized cobalt cubane: ultrafast photophysics probed by transient XUV spectroscopy

The production of renewable solar fuels on a global scale requires the development of water oxidation catalysts from Earth-abundant elements. The tetrametallic oxo-cluster, [CoIII4O4](OAc)4(py)4 (OAc = acetate, py = pyridine), Q1, is a promising molecular compound that has attracted significant interest due to its provocative “cubane” structure and as an especially apposite molecular model for heterogeneous CoOx-based water oxidation catalysis. This work seeks to provide understanding of the electronic structure of Q1 in its neutral and oxidized, ground and excited states. To that end the technique of femtosecond M2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy is used as a metal-sensitive probe in the extreme ultraviolet (XUV) region of the electromagnetic spectrum near 50-90 eV. A new sample preparation method is developed for the production of high-quality thin films suitable for XUV spectroscopy. Both static and transient spectra are collected and are interpreted in terms of oxidation state, spin state, and hole delocalization within the structure by comparison with ligand-field multiplet simulations. In this work is also presented the means of cubane photosensitization using perylene diimide chromophores. Optical transient absorption spectroscopy is used to verify successful electron transfer, and evidence for energy transfer is also observed. It is further found that Q1 ligand-field excitation with green visible light results in rapid singlet→quintet intersystem crossing (ISC) in 38 fs. The merits of exponential vs. non-exponential kinetics to describe these dynamics are discussed, as well as the greater implications for ultrafast ISC in transition metal complexes.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Shari'ati, Yusef A

Contributors dc:contributor

• Vura-Weis, Josh
• van der Veen, Renske
• Fout, Alison
• Olshansky, Lisa

• Ultrafast Spectroscopy
• Extreme Ultraviolet
• Water Oxidation Catalysis
• Photoinduced Electron Transfer
• Cobalt Oxide
• Cubane
• Perylene Diimide

Statement dc:rights

• Copyright 2022 Yusef Shari'ati

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/117830

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F117830