Uncovering New Catalytic Systems in Photochemistry through Rational Design

Photochemistry and photophysics represent a dynamic branch of research that, exploring the interaction between light and matter, connects diverse scientific disciplines including chemistry, physics, materials science, biology, and medicine. In the field of organic chemistry, the advances in understanding molecular behaviour in the excited state during the 20th century have established photochemistry as a powerful synthetic tool. The unique reactivity offered by light excitation enables new transformations that are not accessible under purely thermal conditions. In a photochemical reaction, a catalyst can act as the light-absorbing species (photocatalyst) that, upon light excitation, activates the substrate. Alternatively, it can first interact with the substrate to generate a new intermediate capable of absorbing light. This Ph.D. dissertation explores new catalytic manifolds made possible through the rational design of light-absorbing species. In the first part, it is shown how the formation of catalytically generated iminium ions incorporated into a heteroaromatic framework gives access to their otherwise elusive triplet state, that can be stereoselectively intercepted by alkene reaction partners. The second part focuses instead on the design of new photocatalysts capable of engaging in mechanistically varied synthetic settings. The methods and catalysts presented in this dissertation provide new tools for the selective manipulation of organic substrates, thereby expanding the scope of synthetic photochemistry. This work covers only the research that I carried out at the University of Padova.