Photochemical Sciences Ph.D. Dissertations

Probing the excited state processes with Electron Paramagnetic Resonance spectroscopy

Date of Award

2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Malcolm Forbes (Committee Co-Chair)

Second Advisor

Jayaraman Sivaguru (Committee Co-Chair)

Third Advisor

Hong Lu (Committee Member)

Fourth Advisor

Joseph Furgal (Committee Member)

Fifth Advisor

Judith May (Other)

Abstract

Detecting and analyzing the structure, dynamics, and reactivity of radical intermediates is important in the understanding of the mechanisms of many photochemical reactions and is useful for predicting and developing new reactions. Most radical intermediates are difficult to detect due to their high reactivity and relatively short lifetimes. Steady-state (SSEPR) and Time-Resolved Electron Paramagnetic Resonance (TREPR) spectroscopy have been used successfully to detect and analyze the nature, structure and dynamic motion of photochemically generated radicals. The SSEPR technique is applied to systems involving detection and identification of reactive intermediates, while the TREPR technique is used for analyzing spin dynamics parameters. In addition, using these two techniques, this thesis exploits the use of the spin trapping technique to better understand the mechanisms of photochemical reactions and characterize the nature of any/all intermediate radicals. The first aspect of the dissertation will introduce EPR spectroscopy as a tool to investigate the mechanism of the [2+4]-photodimerization of aryl-maleimides. Instead of an expected [2+2]-photodimerization, these compounds undergo [2+4]-photodimerization under both photosensitized and direct irradiation using visible light excitation. Based on spin trapping experiments, the reaction was established to proceed through a radical mechanism; the details of this phenomenon will be discussed. The second aspect of the dissertation will evaluate the use of EPR spectroscopy to investigate light induced degradation of liquid crystalline materials used in electronically dimmable vision systems. EPR spectroscopy is utilized here to understand the role of various stabilizers in preventing the degradation process. The last aspect of the dissertation will highlight a Time Resolved EPR spectroscopy investigation of the interaction of the Rose Bengal dye’s excited triplet state with a stable radical TEMPO in the presence of surfactant molecules, as a means to create a topological barrier to control spin information transfer.

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