Photosensitization and Analytical Study on Reactive Oxygen Intermediates: Self-sorting Surface Radicals and “On-off” Sensitizer Function Mechanisms

Author

Sarah J. Belh, The Graduate Center, City University of New YorkFollow

Date of Degree

6-2021

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Alexander Greer

Committee Members

Malgorzata Ciszkowska

Alan Lyons

Ryan Murelli

Subject Categories

Analytical Chemistry | Organic Chemistry | Physical Chemistry

Keywords

Alkoxy, peroxide

Abstract

This thesis consists of four chapters which are detailed below. Chapter 1 is an introductory chapter, which lays out the background and purpose of the research.

Chapter 2 describes a study of the mobility of alkoxy radicals on a surface by detection of their recombination product. A novel method called symmetrical product recombination (SRP) utilizes an unsymmetrical peroxide that upon sensitized homolysis recombines to a symmetrical product [R'OOR → R'O•↑ + •OR → ROOR]. This allows for self-sorting of the radical to enhance the recombination path to a symmetrical product, which has been used to deduce surface migratory aptitude. SPR also provides a new opportunity for mechanistic studies of interfacial radicals, including monitoring competition between radical recombination versus surface hydrogen abstraction. This is an approach that might work for other surface-born radicals on natural and artificial particles.

Chapter 3 discusses how photosensitizers rarely function in both light and dark processes as they usually have no function when the lights are turned off. We hypothesized that light and dark mechanisms in an α-diketone will be decoupled by dihedral rotation in a conformation-dependent binding process. Successful decoupling of these two functions is now shown. Namely, anti- and syn-skewed conformations of 4,4′-dimethylbenzil promote photosensitized alkoxy radical production, whereas the syn conformation promotes a binding shutoff reaction with trimethyl phosphite. Less rotation of the diketone is better suited to the photosensitizing function since phosphite binding arises through the syn conformer of lower stability. The dual function seen here with the α-diketone is generally not available to sensitizers of limited conformational flexibility, such as porphyrins, phthalocyanines, and fullerenes.

Chapter 4 shows efforts to increase the number of triplet sensitizer sites in superhydrophobic surfaces, which is key for increasing ¹O₂ output in aqueous phase oxidations. Here, mainly theoretical work is shown with some supporting experimental work. Based on theoretical calculations, the porous particle would provide the highest potential sensitizer population on the superhydrophobic surface. Experimental approaches were used with chlorin e₆ sensitizer adsorbed with porous milliparticles, and nonporous microparticles, and nonporous nanoparticles to determine the weight of particles loaded onto the superhydrophobic surface. Desorption of the sensitizer is found to be a key component.

Recommended Citation

Belh, Sarah J., "Photosensitization and Analytical Study on Reactive Oxygen Intermediates: Self-sorting Surface Radicals and “On-off” Sensitizer Function Mechanisms" (2021). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/4354