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

Shari'ati, Yusef A

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

Description

Title

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

Author(s)

Shari'ati, Yusef A

Issue Date

2022-12-02

Director of Research (if dissertation) or Advisor (if thesis)

Vura-Weis, Josh

Doctoral Committee Chair(s)

Vura-Weis, Josh

Committee Member(s)

• van der Veen, Renske
• Fout, Alison
• Olshansky, Lisa

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• ultrafast spectroscopy
• extreme ultraviolet
• water oxidation catalysis
• photoinduced electron transfer
• cobalt oxide
• cubane
• perylene diimide

Abstract

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.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Yusef Shari'ati

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