Ultrafast electron transfer and intersystem crossing in bimetallic molecules

Burke, John Henry

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https://hdl.handle.net/2142/132786 Copy

Description

Title

Ultrafast electron transfer and intersystem crossing in bimetallic molecules

Author(s)

Burke, John Henry

Issue Date

2025-12-03

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
• Mirica, Liviu
• Makri, Nancy

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Mixed valence
• dimer
• bimetallic
• inorganic
• organometallic
• ferrocene
• metallocene
• MMCT
• IVCT
• charge transfer
• femtosecond
• picosecond
• laser
• photophysics
• transient absorption
• X-ray
• XUV
• absorption
• XAS
• XES
• XANES
• EXAFS
• spectroscopy
• synchrotron
• X-ray free electron laser
• XFEL
• high harmonic generation
• HHG
• chiral induced spin selectivity effect
• CISS
• chirality
• high spin
• quintet
• excited state

Abstract

Increasingly, the role of electron spin is an important topic in electron transfer (ET). Coupling between the electronic, spin, and nuclear degrees of freedom play an important role in driving ET and intersystem crossing (ISC) on the ultrafast timescale. In this thesis, ultrafast optical and X-ray techniques are used to characterize the ET and ISC dynamics of a prototypical bimetallic FeIICoIII molecule following metal-to-metal charge transfer (MMCT) excitation. Femtosecond optical transient absorption (OTA) spectroscopy supported by time-dependent density functional theory (TD-DFT) find evidence of long-lived FeII ligand-field excited states, suggesting that the MMCT state decays by subpicosecond ISC and back ET (BET). Using synchrotron-based K-edge X-ray transient absorption (XTA), the longest-lived excited state is characterized as an FeII high-spin based on the metal-ligand bond elongation evidenced by extended X-ray absorption fine structure (EXAFS). Then, synchrotron-based L-edge XTA is used to show that the shorter-lived Fe-centered excited state is a triplet state that exhibits charge delocalization between the FeII and CoIII centers. This triplet state is further characterized by extreme ultraviolet (XUV) TA with a high-harmonic-generation source. Next, femtosecond hard X-ray experiments are performed with an X-ray free electron laser source to characterize the ultrafast ISC+BET reaction. Kβ X-ray emission spectroscopy provides the oxidation-state and spin-state specificity required to monitor the electronic and spin degrees of freedom during the reaction. In conjunction, K-edge XTA linear anisotropy tracks the geometry changes during the reaction, allowing a view of the vibrational motion in the molecular frame. Then, with this (achiral) FeIICoIII complex thoroughly characterized, we developed a novel chiral analogue to examine effects of chirality on the ISC+BET reaction. Initial UV-vis absorption and OTA experiments show that the chiral substituent minimally perturbs the electronic structure and dynamics of the complex. Furthermore, no changes in the ISC+BET rate are detected within the time resolution of the OTA experiment. Overall, this thesis sheds new light on the coupling between electronic, nuclear, and spin degrees of freedom following MMCT in a bimetallic molecule.

Graduation Semester

2025-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/132786

Copyright and License Information

Copyright 2025 John Henry Burke

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