(2bg) Green Organic Photoredox Catalysis: Electronic Structure Guided Design and Discovery

Several examples of promising organic photoredox catalysts have reemerged recently in the drive to achieve greener catalysis for reactions such as water splitting and CO2 reduction. The structural complexity and complicated degradation pathways of organic photoredox catalysts have limited the implementation and study of these catalysts, even though they have promising redox potentials. Due to the complexity of modeling these catalysts, they are ideal candidates for evolution and discovery via genetic algorithms. Genetic algorithms utilize the genetic footprints (molecular formulas) of ‘parents’ to generate ‘offspring’, which based on applied fitness functions determines the genetic information that passes to future generations. While genetic algorithms are commonly employed in photovoltaic and drug discovery, there are limited examples of machine learning discovery approaches for catalysts, let alone photoredox catalysts. In this study, we develop a fitness function for describing the success of organic photoredox catalysts in efficient, degradation-resistant CO2 reduction based on prior experimental and theoretical studies. Our prior work modelling substituted p-terphenyls for CO₂ reduction identified LUMO energies as a computationally inexpensive descriptor for electron transfer rate. In addition, the de-aromatization reactions that threaten catalytic success are often linked to attack at more anionic positions. Our genetic algorithms utilize average carbon charge, LUMO energies, and an experimentally calibrated excitation energy filter to evolve a pool of substituted oligophenylenes towards catalysts capable of quickly reducing CO2 while resisting degradation. By varying the relative weight of reduction potential versus average carbon charge, we generate 103 unique oligophenylene structures whose sizes and isomeric forms vary greatly. We then perform in-depth electronic structure calculations on all unique catalysts to assess the genetic algorithm’s success in enhancing electron transfer rates and resistance to degradation relative to experimental references and the parent population. Though most catalysts reflect improvement from our benchmarks, we propose 25 most viable catalysts for future experimental study towards CO2 reduction. We also identify a recommended balance between weighting reduction potential and degradation resistance for future catalyst discovery.

Research Interests

Overview: I aim to explore the possibility space of organic photoredox catalysts through a combination of electronic structure calculations, synthesizability and environmental parameter estimations, and experimental validation of efficiency and degradation reactions. The exploration of organic photoredox catalysts could reduce our reliance on metallic catalysts and provide insight into underlying electronic structure properties that enable otherwise challenging chemistry.

Electronic Structure Mechanism Elucidation: Organic photoredox catalysts pose a vastly understudied space with highly structurally sensitive activity and electronic structure properties. Additionally, the degradation reactions which limit the large scale implementation of these catalysts are varied and themselves are underexplored in the context of catalytic applications. In my future work, I want to explore a broader set of catalytic applications for organic photoredox catalysts both theoretically and experimentally to develop insight into common structure activity relationships and the ways cutting edge computational tools can provide detailed electronic structure information about the causes of these relationships. As I work to elucidate the dominant mechanisms of charge transfer, excitation, and catalyst degradation, I will focus on their relevance to catalyst efficiency.

Experimental Verification of Catalyst Activity: To ensure that these predictions are grounded in experimental realities, we will need more experimental research into what degradation reactions limit catalyst activity, which catalysts are efficient, and the synthetic limitations of modifying these catalysts in ways for molecular models. I am currently working part time in Dr. Dawlaty’s experimental group at USC to gain the foundations of experimental characterization of organic photoredox catalysts so that I can perform research which incorporates experimentally guided molecular design.

Synthesizability and Environmental Impact Parameters: Another method for ensuring that any predicted catalysts have a higher chance of experimental success is to include parameters that explicitly describe synthetic ease or environmental toxicity. Recent work in medicinal chemistry has focused on developing programs that can provide parameters such as the number of synthetic steps or synthesis solvents for use in machine learning discovery efforts. Extending these tools to discovery efforts in organic photoredox catalysts will improve the experimental viability of predicted catalysts. Similar programs describing environmental impacts of proposed catalysts or catalytic systems are also becoming increasingly popular and will become valuable in reducing the indirect environmental impact of predictions if they are included in catalyst discovery efforts. I presented at and participated in the ACS Green Chemistry Summer School in 2021 and am focused on incorporating recommended green chemistry practices into our design and discovery of organic photoredox catalysts.

Teaching Interests

Course Design: I am excited by the possibility of incorporating molecular modeling software into kinetics and thermodynamic courses at the graduate level and into undergraduate courses that discuss reaction mechanisms, kinetics, and selectivity. Through my research I have seen the advantage of approaching molecular modeling as a tool available to students for understanding chemical reactions and property trends. While in my PhD, I developed lesson plans and training webinars for high school teachers to incorporate IQMol into their courses to give students a hands-on tool for understanding the chemical trends often covered in high school courses. Similar lesson plans or even a separate elective course could help chemistry and chemical engineering students better understand the electronic origins of commonly studied reactions. I would be interested in incorporating these tools into more general courses as supplements and designing electives which focus on understand quantum chemical modeling efforts and their relevance to catalyst and reaction design. I am also deeply interested in green chemistry practices and the historical connection between the efforts of chemical engineers and the environmental health of our planet. Having a course which focused on the history of chemical engineering in the context of specific and still very industrial relevant chemical processes would strengthen student’s understanding of the origin of current industrial best practices and their role in improving the sustainability of their research. Additionally, I believe that courses focused on research best practices and the mechanisms of academic research could help address inequalities in student backgrounds by explaining how research is conducted and how those processes are the result of historical best practices and the drive for more innovative work. Specifically including opportunities to conduct and present on small research projects and reflect on the stages of that process could help students from less technically privileged backgrounds approach their future research. Including group projects and active learning into all of my courses will also help increase student engagement and retention. I have taken several education courses focused on environmental education and best practices in pedagogy and I look forward to exploring how these best practices can help students connect their academic studies to skill development that supports their professional and academic careers.

Leadership in Outreach: In addition to my academic research, I have been heavily involved in leadership positions in student organizations, education outreach, and department activities at USC. I helped found a chapter of Women in Chemical Engineering at USC in 2019 and have served in various leadership positions on the executive board since, including president and outreach coordinator. I have also served as Outreach Coordinator and Graduate Representative in USC’s chapter for Queers in Engineering, Science and Technology. As Outreach Coordinator, I have planned fundraisers for local LGBTQ Centers and have organized professional and academic development events for graduate and undergraduate students. I presented a talk and a poster at the oSTEM national conference and am helping plan and run the SoCal oSTEM regional conference at USC, including planning fundraisers, workshops, and poster sessions with the overall goal of improving the visibility and community of queer scientists. My interest in academia has also motivated me to pursue a Certificate for Excellence in Teaching through USC’s education program and to serve on committees reviewing LGBTQ inclusive practices in course design, which yielded faculty guides.

Overview: I intend to continue my exploration of both research and pedagogical best practices so that I can develop courses and research programs that support students and help them develop themselves as members of a research or industrial community where valuing diversity is a critical component of innovative science and engineering. I am particularly interested in incorporating the active use of molecular modeling as a general tool for understanding chemical mechanisms and reactivity in a variety of graduate and undergraduate courses.