Investigating the excited-state landscape of photosensitizers based on earth-abundant metals

Details

Supervisors

Troian-Gautier, Ludovic

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité approfondie

Abstract

enIn recent years, photochemistry based on metal complexes has gained significant momentum with applications in different fields of chemistry. While early developments focused on rare and expensive metal centers such as ruthenium, rhodium, and iridium, research has increasingly shifted towards more sustainable alternatives based on Earth-abundant metals like chromium, iron or copper. However, this transition comes with substantial trade-offs in photophysical performances, requiring innovative design strategies to reach their full potential. This thesis investigates the excited-state landscape and relaxation pathways of Co(III) and Mn(IV) photosensitizers bearing a tridentate N-heterocyclic carbene ligand developed by Smith and coworkers in 2006. Despite demonstrating potentially promising properties for a broader application, both systems suffer from key limitations, namely, the weak visible-light absorption in the cobalt complex and the multitude of accessible excited states in the manganese analogue with significant energy loss upon relaxation to the lowest excited state. To address these issues, this work presents a comprehensive study combining steady-state and time-resolved spectroscopy, electrochemical characterization, and bimolecular quenching experiments. In particular, the energy required to sensitize the long-lived 3MC state of the cobalt complex was experimentally estimated. For the manganese complex, the first experimental evidence of successful energy harvesting from a high-lying excited state was obtained. The findings not only provide new insights into the photophysical behavior of these systems but also establish a foundation for future optimization via covalently linked dyad architectures designed to enhance visible-light harvesting and excited-state reactivity.