| dc.description.abstract | Dirhodium (II,II) molecules are an extensively studied class of metal-metal bonded compounds. The population of a long-lived triplet excited state (3ES) allows for these complexes to be used as photosensitizers for applications such as photodynamic therapy (PDT) or in the construction of dye sensitized solar cells (DSSCs).
Dirhodium partial paddlewheel complexes featuring electron donating bridging ligands and electron accepting chelating diimine ligands have been shown to act as excellent PDT agents due their ability to bind and photocleave DNA as well to generate 1O2 upon irradiation. A mixed bridging ligand compound, [Rh2(F2Form)(OAc)(dppn)2]2+ (2; F2Form = N,N’-2,6-o-difluoroformamidinate, dppn = benzo[i]dipyrido[3,2-a:2’,3’-c]phenazine) was prepared from the starting material Rh2(F2Form)(OAc)3 (1) which is the first such partial paddlewheel of its kind with a 1:3 ratio of different bridging ligands. Compound 2 has a relatively high singlet oxygen quantum yield of 0.58(8) and, upon irradiation with visible light, photocleaves plasmid DNA and induces cell death via apoptotic and necrotic mechanisms. The photocytotoxicity of 2 against HeLa cells was found to increase by a factor of 25.3 upon irradiation with visible light, an impressive increase compared to related compounds. The mixed bridging ligand motif is a promising platform for the development of novel Rh2-based photosensitizers for PDT applications.
Exploration of the functionalization of the bridging formamidinate ligands was undertaken by systematic investigation of the effect of halogen substitution on the photophysical properties of the dirhodium complexes. The bridging ligands F-Form, Cl- Form, Br-Form and I-Form were used in the synthesis of series of a homologous series of dirhodium complexes. Single crystal X-ray diffraction, DFT calculations and time-dependent NMR studies revealed differences in the lability of coordinating solvent ligands and trends in electronic structure.
The ability to functionalize the coordinating ligands of the dirhodium core allows for convenient modification of the complex for other applications. Carboxylic acid functionalized, axial blocking ligands were used to prepare formamidinate bridged dirhodium complexes. The carboxylic acid substituent allows the complexes to bind to TiO2 or NiO and act as photosensitizers in the construction of dye-sensitized solar cells. Methods to tune the coordinating ligands and improve the photosensitizing properties of these complexes as well as to introduce new functionalities are described in this dissertation. | |
