Authors: Kakra, Benjamin Kwesi
Source: Scholarship & Creative Works - Digital UNC a service of University Libraries (University of Northern Colorado) (article, 2025-08-01)
Field: Chemistry — Organic Chemistry

Development of Polymer-Supported Organic Photoredox Catalysts Photoredox catalysis has been a useful tool that has replaced the traditional method of synthesis because of its ability to support reactions that are difficult to carry out under traditional reaction conditions (Nicholls et al., 2016). As traditional methods of synthesis are considered to be environmentally unsustainable and expensive, photoredox catalysis has been known to align well with environmental sustainability and is also cost-effective (Shaw et al., 2016). Photoredox catalysis has been used not only in synthesis but also in carbon dioxide reduction and water purification (Venditto et al., 2024). The method only requires light as a source of energy and a suitable molecule that effectively interacts with light, usually known as a photoredox catalyst, to make transformations occur (Shaw et al., 2016). Complexes of precious transition metals were initially used as photoredox catalysts (Haria & König, 2014). However, they had some limitations, which led to the development of organic photoredox catalysts (Bobo, Kuchta, et al., 2021). Organic photoredox catalysts, especially strongly reducing molecules such as phenoxazines, offer greater stability, lower cost, and improved selectivity (Nicewicz & Nguyen, 2014). These molecules are sensitive to any structural modification, and the type of solvent they are present in, which changes their properties and performance. Various structural modifications have been done on these molecules to fine-tune their properties and performance. However, the modifications result in the discrete form of these molecules, which makes them difficult to recover and reuse (McCarthy et al., 2018). Immobilizing them on polymer supports can enhance performance, recovery, and recyclability (Sridhar et al., 2019). As such, this study focuses on the development and characterization of polymersupported photoredox catalysts (PS-PCs) as a sustainable tool for photochemical transformations. A library of PS-PCs based on phenoxazine was synthesized, incorporating both N-aryl and core-functionalized phenoxazine photoredox catalysts into cyclooctene polymer backbones. These photoredox catalysts were characterized for their photophysical and thermodynamic properties, including solubility, solvatochromism (ability of the PS-PCs to change color in solvents of different polarity), polymer weight and dispersity, absorption, and emission behavior. The performance of the PS-PCs was evaluated in model photochemical reactions, specifically bromoalkylation and cyclopropanation of unactivated alkenes, to assess their reactivity and recovery potential. The results revealed the success of the catalyst's recovery and the solvatochromic behavior of the PS-PCs. It also demonstrates that while the absorption profiles of the PS-PCs did not significantly influence their catalytic activity, the emission profiles, molecular weight, and dispersity played critical roles in determining their performance. Notably, PS-PCs with lower molecular weight and narrower dispersity exhibited superior catalytic efficiency, particularly in the bromoalkylation reaction. This work emphasizes the potential of PS-PCs as greener tools for organic synthesis. Photoredox catalysis ; Catalysis ; Green chemistry ; Molecule ; Environmentally friendly ; Organic molecules ; Organic synthesis Radical Photochemical Reactions ; Advanced Photocatalysis Techniques ; Nanomaterials for catalytic reactions