Chapter 1 introduces the research discussed in this thesis. An overview of state-ofthe- art approaches to photocatalytic hydrogen evolution is included. The focus is on ruthenium-platinum/palladium intramolecular systems, with a goal towards immobilising the complexes onto surfaces. Included in this section are the techniques employed, throughout the research carried-out, to probe the steps leading to hydrogen generation. Chapter 2 explores the intermolecular route towards hydrogen generation using a known photosensitiser, a Ru-diphenylphenanthroline (dpph) complex, [Ru(dpph)3](PF6)2. This photosensitiser was irradiated under multiple reaction conditions, systematically investigating the effect of each on the turnover number. Substitution of one of the of ligands with a suitable bridging ligand (BL) was achieved ([Ru(L)3] → [Ru(L)2(BL)]), enabling synthesis of a photocatalyst capable of intramolecular hydrogen production ([Ru(L)2(BL)PtI2]). These complexes were investigated for their hydrogen production capabilities. Time resolved studies spanning the pico- to –millisecond time scale were carried out both at DCU and with collaborators in the University of Twente. Chapter 3 compares a known working terpyridine ruthenium photocatalytic assembly with a novel triazole-photocatalyst. Photocatalytic studies were performed, and in an attempt to probe the photochemical steps leading to hydrogen generation, time resolved transient absorption and time resolved infrared were carried out. The experiments were conducted both in solution and following adsorption of the ruthenium-platinum/palladium complexes onto NiO. Together with collaborators at the University of Newcastle photoelectrocatalytic hydrogen evolution studies were performed. Chapter 4 introduces the use of Ru-M complexes as photosensitisers for photocatalytic CO2 reduction studies, where M = Re-carbonyl moiety. This chapter also introduces intramolecular assemblies based on porphyrin-Re-carbonyls were assessed for their ability to reduce CO2 to CO. Time-resolved and photocatalytic studies were conducted. Chapter 5 gives a brief literature review of boron-dipyrromethene based monomeric and polymer compounds. These compounds were assessed for their ability to generate singlet oxygen. Time-resolved IR studies together with transient absorption measurements were performed to probe the mechanism leading to formation of this cytotoxic species. Chapter 6 contains concluding remarks and future work for each chapter.