The adverse impacts of climate change and global warming on the environment such as, air pollution and deforestation must be mitigated, and renewable sources of energy must be more frequently employed. Chapter 1 focuses on the scale of greenhouse gas emissions, and it explores solutions for sustainable energy. The primary approach proposed in this thesis involves photocatalytic hydrogen evolution and carbon dioxide valorisation, which can be successfully carried out in laboratory settings using a variety of photosensitisers and photocatalysts. Key components of the photocatalytic processes are described along with photophysical and electrochemical measurements for the analysis of compounds synthesised in this dissertation. Chapter 2 includes a literature review focussed on the synthesis, photophysical and electrochemical properties of naphthalene diimide (NDI)/perylene diimide (PDI) ruthenium complexes. The review provides a rationale for why Ru-NDIs/PDIs compounds can be utilised for photocatalysis. A ruthenium-naphthalene diimide donoracceptor system (RuNDI2+) was synthesised for hydrogen evolution (Chapter 3). The complex was investigated using photophysical and electrochemical techniques, including time-resolved infrared spectroscopy (TRIR) and nanosecond-transient absorption spectroscopy (TAS), spectroelectrochemistry and electrochemistry. Furthermore, photoactive intermediates formed during photocatalysis and their photophysical characteristics were investigated. In Chapter 4, the Ru(dceb)-NDI2+ (4,4′-di(carboxyethyl)bipyridine ruthenium-naphthalene diimide) photosensitiser was synthesised for hydrogen evolution. Incorporation of the peripheral ester groups was observed to influence the photophysical, electrochemical and spectroelectrochemical properties, as well as hydrogen evolution in comparison to the bipyridine analogue studied in Chapter 3. In Chapter 5, a range of Ru-NDI complexes were investigated using TRIR and TAS, where the impact of different functional groups on their photophysical properties was studied. In Chapter 6, the synthesis, photophysical and electrochemical properties of porphyrin-naphthalene diimide compounds are presented. The Rehm-Weller approach was used to determine the thermodynamic driving force for hydrogen evolution.