Studies on photoactive ruthenium(II) and iridium(III) polypyridyl complexes

Abstract

This thesis reports studies into several photoactive transition metal complexes. The photochemistry of [Ir(tpy)Cl3], hitherto used mainly as a synthetic precursor in thermal reactions, is reported in Chapter 2. Results showed that photosubstitution occurred under light, with solvent replacing one chloride ligand to give [Ir(tpy)(S)Cl2]+, where S is solvent (H2O, MeOH, MeCN). Two isomeric photoproducts were discovered in DMSO: one identified as [Ir(tpy)(kS-DMSO)Cl2]Cl (2A) and the other as [Ir(tpy)(kO-DMSO)Cl2]Cl (2B). 2A was the primary product under green light (505nm), whereas 2B predominated at long-wave UV wavelengths. Furthermore, these isomers could interconvert photochemically in a bi-directional linkage isomerism process that could be cycled at least five times over 250 hours without evidence of photodecomposition. Instances of photoswitches with photochemically driven forward and reverse processes such as this are relatively uncommon and lead to promising applications, e.g. in erasable information storage. Further study showed the conversion of 2A to 2B was an intermolecular process, and that 2A was also photoactive in other solvents. The photobiological activity of [Ir(Menphen)2Cl2]Cl (n=0, 2 or 4)] is reported in Chapter 3. Cytotoxicity was determined both with and without irradiation, against several cancer cell lines, and intra-cellular accumulation was tracked using fluorescence microscopy. The complexes accumulated mainly in lysosomes, and their toxicity increased under light (>390nm). [Ir(Me2phen)2Cl2]Cl showed promise as an effective light-activated anticancer agent and we recommend further biochemical studies with this complex. Further biological testing, including cell cycle analysis and protein expression, indicated that these complexes are probably very similar to so-called cationic amphiphilic drugs (CAD), which have been shown to have some efficacy against cancer, but also potentially harmful side effects. For these iridium complexes, CAD characteristics are only activated under light, which increases selectivity. Chapter 4 investigates the photocytotoxicity of mononuclear Ru(II) complexes with and without the tetradentate ligand bb7, which could increase structural strain and thereby enhance photochemistry. We found instead that these structures remained relatively unstrained with no enhancement in their photoactivity. However, [Ru(Me4phen)3]2+ was found, for the first time, to have promise as a photoactive anticancer agent