Development of Iridium Based Photosensitizer for Potent Photoreductants and Photocatalytic Application

This dissertation describes the development of iridium based organometallic photosensitizers which function as potent photoreductants for photoredox catalysis. Chapter 1 describes the basic concepts of photosensitizers in photocatalysis and strategies to modify the photophysical and electrochemical properties via ligand modification with different types of photosensitizers. Chapter 2 describes the first generation of bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ligands. The photophysical and electrochemical properties were compared to fac-Ir(ppy)3, known to be a ‘the-state-of-the-art’ photoreductant, and the calculated excited-state potentials (ESPs) show that our complexes have more reductive potential than fac-Ir(ppy)3. Stern-Volmer quenching experiments also support that the new complexes have higher ESP and reducing ability. Chapter 3 describes an expanded photocatalyst library with further modified NacNac ligands. Based on results from Chapter 1, we have prepared a dozen photosensitizers for the photocatalytic hydrodebromination of bromide substrate and we have screened to find the best-optimized conditions to activate the carbon-bromine bond to replace with a hydrogen atom. Chapter 4 is a deeper study of the hydrodehalogenation reaction with candidate photosensitizers from Chapter 3. Under modified and optimized reaction conditions, alkyl and aryl halides (X = Br, Cl, F) are tolerated in hydrodehalogenation and functionalization reactions proceeding through a radical-mediated reaction mechanism. Finally, Chapter 5 describes the second ligand modification strategy to elevate the excited-state energy (ET1) with alternative cyclometalating ligands which have been used for blue-emitting compounds. Replacing the cyclometalating ligands that we previously used with triazole or NHC-derviced cyclometalating ligands results in a highly destabilized LUMO energy level and record-high excited-state potentials for cyclometalated iridium photosensitizers.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Houston

Year dc:date.issued

2020

Author dc:creator

• Shon, Jong Hwa

Advisor dc:contributor.advisor

• Teets, Thomas S.

Committee members dc:contributor.committeemember

• Halasyamani, P. Shiv
• Miljanić, Ognjen Š.
• Brgoch, Jakoah
• Bao, Jiming

• Photoreductant, photoredox catalysis, photocatalyst

Statement dc:rights

• The author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/10657/10269

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/10269