Triplet state access in multi-component heavy atom free photosensitizers in photomedicine

Photodynamic therapy (PDT) has been a known clinical treatment for cancer for at least 30 years. The scientific community has since aimed to improve the therapeutic efficacy of PDT. This thesis describes a comprehensive study into recent advances made towards improving the drug candidates (photosensitizers) for this therapy. A novel and exotic triplet forming mechanism called triplet formation via charge recombination, is described in detail. This mechanism has the potential to pave the way for a new generation of photosensitizers. The rest of the thesis includes a study into the application of improved photosensitizers. More specifically, a tetra(hexyloxy)phenylporphyrin was synthesized and made into a thin film. Singlet oxygen production was detected from this thin film and moreover, photosensitizers (PSs) containing kraft lignin have been synthesized, modified and studied with time-resolved and steady-state spectroscopy techniques, to determine their potential in photomedicine. Furthermore, a novel porphyrin-cyanine dye conjugate was created and analyzed for its potential in PDT and it appears that there is some triplet formation via charge recombination occurring. Furthermore, synthetic methods used to create new porphyrin and cyanine dyes are discussed as well as the photophysical characterization of 16 novel phenalenone PSs. The photophysical properties were compared to their efficacy against gram-positive and gram-negative bacteria. Overall, this thesis has provided novel photosensitizers and it is clear that some of these, especially the porphyrin-near-IR cyanine dye conjugate, could pave the way for a new generation of PSs.