From molecules to materials: light-activated systems for photocatalytic solar energy conversion

The growing global demand for sustainable energy calls for systems capable of efficiently harvesting solar radiation and storing it in chemical fuels. Artificial photosynthesis offers a promising strategy to convert sunlight into energy-rich molecules through photocatalytic redox reactions. In this context, CO₂ photoreduction to carbon-based fuels and the photocatalytic hydrogen evolution reaction (HER) are central processes, enabling carbon circularity and the generation of a zero-carbon energy carrier, respectively. Both reactions, however, face substantial kinetic and thermodynamic challenges due to their multielectron and proton-coupled nature. The first part of this thesis investigates fully molecular supramolecular assemblies based on a Ru(bpy)₂(CN)₂ chromophore, which serves as a versatile light absorber and coordination platform through its cyanide ligands. In combination with a heptacoordinated Fe(II) polypyridyl catalyst, a stable Ru–Fe supramolecular complex forms in solution, promoting efficient intramolecular electron transfer and highly selective visible-light-driven CO₂-to-CO conversion. The same design concept is extended to proton reduction by replacing the iron catalyst with a cobalt polypyridyl complex. The resulting Ru–Co assembly exhibits strong ground-state association and fast charge transfer, enabling sustained hydrogen evolution in solution in the presence of suitable sacrificial donors and proton sources. Moving toward device-relevant systems, the second part of the thesis explores hybrid architectures that merge molecular photosensitizers with heterogeneous catalysts. In a dynamic hybrid system, a molecular chromophore operates synergistically with a semiconductive nanoparticulate catalyst to drive proton reduction, combining molecular tunability with enhanced catalytic robustness. Finally, a hybrid double-cable system based on a polymeric donor incorporating a molecular electron acceptor and a platinum cocatalyst is presented, where controlled charge-transport pathways enable efficient hydrogen production. Overall, this work elucidates structure–function relationships governing photocatalytic fuel generation across molecular and hybrid systems, highlighting general design principles to enhance charge separation, accelerate multielectron catalysis, and improve photoconversion efficiency.