Quantum mechanical modeling of photochemistry in complex environments

Reiter, Sebastian (2025): Quantum mechanical modeling of photochemistry in complex environments. Dissertation, LMU München: Fakultät für Chemie und Pharmazie

Abstract

Quantum chemical and classical calculations have become an indispensable part of modern chemistry. A persistent challenge for computational methods is the description of weak molecular interactions as they occur in complex environments such as in solution, in catalyst-substrate assemblies, or in biomolecular contexts. This thesis presents a series of methods and applications where such environmental effects play a crucial role. The first chapter focuses on organic photocatalysis with an emphasis on the formation of dispersive ground-state preassemblies between catalyst and substrate in condensed phase. By exploring the catalytic mechanisms through a series of high-level electronic structure calculations, preassemblies are found to open new pathways in two conceptually different types of chemical transformations. These reactions include on the one hand the electromediated photoredox conversion of phosphinated alcohols to carbanions by naphthalene monoimide type catalysts and on the other hand the photochemical C-H arylation of pyrroles via 3d-transition metal complexes. The second chapter presents a multiscale workflow to include atomistic environmental effects in quantum dynamic wave packet simulations by sampling the potential energy surface over the course of a molecular dynamics trajectory. Using this method, the ultrafast S2/S1 relaxation in uracil is found to be strongly affected by embedding the nucleobase in an RNA strand, with a trend towards slower relaxation times. The third chapter of this thesis deals with the topic of artificial photosynthesis. First, the acid-strength dependent catalytic H2 generation via a cobalt-complex with the redox-active Mabiq ligand is investigated using high-level DFT/MRCI calculations. In the future, H2 evolving catalysts like Co(Mabiq) could be combined with natural photosystems, which would act as highly efficient photoactivated electron donors. This requires (a) a better understanding of the light-harvesting process and (b) an option to protect the photosystem against harsh environments while retaining or even enhancing its function. This work thus introduces a new computational model of the excitonic network in cyanobacterial photosystem I, which captures the molecular dynamics of the nanoscale system and describes the complex photophysics of chlorophyll in its natural environment at the DFT/MRCI level. This model is finally used to explore the structural and electronic effects of encapsulating photosystem I in the metal-organic framework ZIF-8. Taken together, this thesis emphasizes the importance of including complex environmental effects in the computational description of molecular transformations. The presented case studies deepen our understanding of a broad range of photophysical and -chemical processes, introducing new photocatalytic strategies in organic synthesis, exploring the photostability of the genetic code, and paving the way toward artificial photosynthesis.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: photochemistry, multiscale modeling, photosynthesis, photocatalysis, computational chemistry
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 540 Chemie
• Fakultäten: Fakultät für Chemie und Pharmazie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 27. Februar 2025
• 1. Bericht­erstatter:in: Ochsenfeld, Christian