Photoredox catalysis is an emerging and powerful methodological approach for accomplishing bond constructions in organic chemistry and utilizes photosensitizers to convert photon energy into chemical potential to drive photo-induced C–C/C–X couplings and C–H bond activations. Given catalysis can be light-activated, this methodology is considered environmentally friendly and sustainable. To date, the three main modes of action are: 1) single electron transfers (SETs) to initiate radical coupling reactions; 2) SETs to simultaneously generate free radicals and activate transition metal catalysis (i.e., dual photoredox); and 3) energy transfer to or direct excitation of a transition metal catalyst. While the number and complexity of bond transformations is rapidly increasing, there are few spectroscopic or computational studies of photoredox mechanisms, largely due to the complexity and interplay between excited state dynamics and reactive intermediates. The applicant will use a variety of high-level spectroscopies spanning 10 orders of magnitude in photon energy and 15 orders of magnitude in time to observe molecular events from femtoseconds after light absorption to individual steps in the reaction. Experimental data guide ligand design to tune ground and excited state structure, regioselectivity, or alter reactivity for new bond constructions. Together, the methodologies allow to evaluate energetics of reaction coordinates, define mechanisms, estimate redox activity of intermediates, and map excited state potential energy surfaces to define key electronic contributions from frontier molecular orbitals. This work will be communicated at local, national, and international seminars and conferences. Major findings will be disseminated via publication in high-impact scientific journals. Importantly, the applicant’s training at the host institution and the returning phase will be invaluable for accomplishing his goal to obtain a position at a major European University.