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 as generate ¹O₂upon irradiation. The bridging ligand N,N’-2,6-o-difluoroformamidinate (F₂-Form) was used in the synthesis of two new series of the type [Rh₂(F₂Form)(OAc)(NN)]²⁺ and [Rh₂(F₂Form)₂(NN)]²⁺, where NN=1,10-phenathroline, dipyrido[3,2-f:2',3'-h]-quinoxaline, dipyrido[3,2-a:2’,3’-c]phenazine, and benzo[i]dipyrido[3,2-a:2’,3’-h]quinoxaline. Formamidinate bridging ligands pose an advantage over acetate bridging ligands due to their increased electron donating capabilities, resulting in a red-shift of the absorbance of these complexes which is favorable for PDT applications. Dirhodium (II,II) complexes featuring the mixed bridging ligands are unique and unexplored for their biological and photophysical properties. This investigation serves to compare and contrast the mixed bridge ligand series [Rh₂(F₂Form)(OAc)(NN)]²⁺with the bis F₂-Form bridged complexes [Rh₂(F₂Form)₂(NN)]²⁺and the bis acetate bridged complexes [Rh₂(OAc)₂(NN)]²⁺. DNA photocleavage experiments and Resazurin cell viability assays were performed, showing great difference in LC₅₀ irradiated versus LC₅₀ in the dark. Cell microscopy and flow cytometry studies with HeLa cells were also performed to elucidate the mechanism of action of these dirhodium complexes.

Kim Dunbar

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