The conversion of solar energy to chemical feedstocks in dye-sensitised photoelectrochemical cells functionalised with molecular catalysts offers an attractive route to mitigate the current energy crisis and reduce global CO₂ emissions. However, most reports currently focus on precious metal-based light absorbers, thus limiting the wide-scale implementation of this technology.

In this dissertation, the use of metal-free diketopyrrolopyrrole (DPP) chromophores has been explored as an alternative to precious metal-based dyes on dye-sensitised photoelectrodes. Firstly, the synthesis of a dyad photocatalyst consisting of a DPP chromophore and ruthenium-based water oxidation catalyst is described. The dyad features suitable light absorption in the visible region and photoinduced hole transfer from the dye to the catalyst unit. Immobilisation of the dyad on a mesoporous TiO₂ scaffold was optimised, and the production of O₂ was confirmed by controlled potential electrolysis. This study demonstrates that metal-free dyes are suitable light absorbers in dyadic systems for the assembly of water-oxidising photoanodes.

As an alternative to O₂ evolution, DPP chromophores with different anchoring groups were synthesised and co-immobilised with an organic nitroxyl radical catalyst on a mesoporous TiO₂ scaffold for light-driven alcohol oxidation. The fully assembled system allowed for efficient conversion of the substrate to the corresponding aldehyde with photocurrents sustained over a 26 hour period with high faradaic efficiency. This work demonstrates the construction of stable precious metal-free dye-sensitised photoanodes, capable of outperforming precious metal-based systems. The photoanode was then wired to a biohybrid cathode modified with the redox enzyme formate dehydrogenase for CO₂ reduction to formate. The reported system is the first example of a photoelectrochemical cell achieving simultaneous CO₂ reduction and chemical synthesis in the absence of an applied bias.

Finally, the synthesis and characterisation of a designer-DPP chromophore for dye-sensitised photocathodes in aqueous media is reported. The chromophore was immobilised on a novel mesoporous CuCrO₂ delafossite scaffold, capable of achieving high photocurrents in the presence of an electron acceptor. After establishing a suitable dye-sensitised platform, the incorporation of molecular catalysts for CO₂ reduction was investigated. A phosphonic acid-functionalised cobalt(II) terpyridine complex was selected, and the method for the co-immobilisation of both components on the CuCrO₂ scaffold was explored. The photoelectrochemical activity of the system was further evaluated under different applied potentials. Although product formation was not detected in any of the studied configurations, a detailed overview of the possible limitations and directions for further development is provided.

This work expands the use of organic dyes for artificial photosynthesis with the aim of replacing ruthenium-based chromophores, and in closing, future directions for the continued development of precious metal-free dye-sensitised systems for solar fuel production are discussed.