Design, synthesis and transformation of new photoactive compounds for photocatalytic applications

In view of the current severe climate crisis and increasing resource scarcity, our society is in urgent need for new strategies to generate fuels, chemicals, and materials from renewable feedstocks. In the interest of future generations, actions need to be taken to develop more efficient transformations solely relying on renewable energy and without the emission of hazardous substances. In this context, photocatalysis as a direct sunlight-driven process has the potential to contribute to a sustainable economy that combines both synthesis and chemical recycling of various chemicals, materials, and fuels. Indeed, excited states generated by light enable thermodynamically uphill reactions, which forms the basis for solar energy storage into fuels. Furthermore, photocatalysis allows the development of novel reaction routes via excited-state reactivity that are inaccessible following ground-state catalytic pathways. Within this framework, this Ph.D thesis explore the application of photocatalytic prosses in the field of artificial photosynthesis and synthetic chemistry. The main part of the research activity focused on Dye-Sensitized Photoelectrochemical Cells (DSPECs) for water splitting, a promising technology for converting solar energy into chemical energy. In this approach, sunlight is captured by a dye and used to promote the photo-oxidation of water (catalyzed by a water oxidation catalyst or WOC), producing 8solar9 fuels such as hydrogen (H2). In this regard, we worked on the modeling, synthesis, and characterization of novel metalfree organic dyes. First, two families of donor-auxiliary acceptor-π-acceptor (D-A-π-A) sensitizers were designed: compounds 1a-c with a 2,3-diphenylquinoxaline core, and compounds PP2a-c with a 2,3-diphenylpyrido[3,4-b]pyrazine core. These dyes were successfully synthesized and characterized spectroscopically and electrochemically. Furthermore, the ability of compounds 1ac to function as anodic sensitizers was evaluated through photo-electrochemical tests in a threeelectrode cell, showing promising results, with compound 1a demonstrating the highest photocurrent generation. Afterward, we turned our attention to alternative dye/catalyst photoanode-sensitization strategies, moving beyond conventional co-loading methods. Here, a novel metal-free sensitizer-catalyst covalent adduct (dyad) was designed, building on the structure of dye 1a and modifying it to enable coordination with the Ru(bda) WOC. This led to the successful synthesis of dyad D1A2, whose obtainment was supported by a full spectro-electrochemical characterization. In addition to this main subject, as a final part of this research work, we also explored the potential of near-ultraviolet and visible light irradiation as a powerful mean in synthetic chemistry. In particular, we investigated novel methodologies for N-functional groups migration on aromatic rings, facilitating the conversion of aryl azides into anilines with regioisomeric substitution patterns.