Supported homogeneous photocatalysis using new organic chromophores and silica nanoparticles

The abounding environmental issues of our time have pushed sustainability at the forefront of scientific research. Due to the surging energy demand, many researchers are turning to clean and renewable resources such as solar power. In chemistry, light driven processes have been blooming through photocatalysis, a valuable tool for implementing greener strategies. Ruthenium and iridium-based polypyridyl complexes are prominent photocatalysts but their rareness, elevated cost, and toxicity can be onerous. Alternatives, such as fully organic photocatalysts, have been researched and could constitute adequate replacements. However, due to the homogeneous nature of these molecules, effective recycling of organic photocatalysts is often complex. The aim of this master thesis consisted in the development of a recyclable and accessible photocatalytic system, applicable to organic synthesis. Throughout this research project, a new set of organic chromophores, based on benzophenazines, were developed. Their synthesis was achieved with a straightforward two-step pathway and their visible-light-absorbing property was briefly characterized with UV-visible spectroscopy. Photocatalytic activity was benchmarked through the photooxidation of citronellol. The tested chromophore displayed excellent photocatalytic conversions of up to 96 %, hence confirming its photocatalyst status and highlighting the value of this kind of molecule in organic synthesis. A theoretical study was performed to reach a finer understanding of the molecules’ properties as well as establish a structure-activity relationship. It was found that photocatalysts with electron donating groups on their southern moiety tend to absorb at longer wavelengths, which is desirable for reaching lower energy activation. As for the support, silica nanoparticles were synthesized and functionalized using APTES to obtain amine moieties. Immobilization of the organic photocatalyst was successfully carried out with the help of coupling agents, DCC and DMAP. The resulting heterogenized photocatalyst was tested using the same benchmark reaction as the homogeneous tests. The silica-supported catalyst was tested over two runs and displayed remarkable photocatalytic activity of up to 97 % conversion as well as improved resistance to photodegradation. These findings attest the utility of heterogenizing homogeneous photocatalysts for obtaining greener catalytic systems.