Thesis presented March 28, 2023

Abstract:
This thesis is devoted to the development of molecular or hybrid (molecular/inorganic) photocatalytic systems for the photo-induced reduction of protons to dihydrogen (H₂) in purely aqueous solution. The aims were: to identify new efficient and robust catalysts for H₂ evolution, to increase the stability and efficiency of existing photosensitizers and finally to test new photosensitizer/catalyst combinations.
A new rhodium complex with a terpyridine ligand ([Rh(tpy)(CH₃CN)Cl₂]⁺) was first isolated and characterized. This complex showed interesting performance as a catalyst for H₂ production under visible light irradiation in the presence of the benchmark photosensitizer, the ruthenium tris-bipyridine complex ([Ru(bpy)₃]²⁺) and ascorbate as a sacrificial electron donor. In order to increase the stability of the catalytic systems using the photosensitizer [Ru(bpy)₃]²⁺, the latter was substituted by the water-soluble ruthenium tris-dibenzenesulfonate-phenanthroline complex ([Ru((SO₃Ph)₂phen)₃]^4-) which exhibits a twofold higher absorption coefficient and a longer lifetime of its excited state while maintaining quite similar potentials. Combined with a tetraazamacrocyclic cobalt catalyst ([Co(CR₁₄)Cl₂]⁺) and ascorbate, this photosensitizer was shown to be more stable leading to a higher H₂ production during photocatalysis compared to [Ru(bpy)₃]²⁺, with nearly 5000 catalytic cycles performed per catalyst molecule in 24 h of irradiation. The last part of this manuscript describes hybrid systems combining inorganic photosensitizers based on semiconductor nanocrystals of cadmium-free CuInS₂/ZnS quantum dots with a molecular catalyst. In order to increase the emission quantum yield of the CuInS₂/ZnS quantum dots, the CuInS₂ core of the latter has been doped with zinc. It was also shown that these quantum dots are capable of activating, in addition to the tetraazamacrocyclic cobalt catalyst, other families of catalysts for H₂ production such as rhodium with polypyridinyl ligands and nickel complexes with phosphine ligands.

Keywords:
Photocatalytic production of dihydrogen, H₂ evolving molecular catalysts, Molecular photosensitizers, Cadmium-free Quantum Dots, Three-component photocatalytic systems