BODIPY-ruthenium(II) polypyridyl complexes: Synthesis, computational, spectroscopic, electrochemical, and singlet oxygen studies

Three BODIPY dyes with 4-phenylpyridyl or 4-pyridyl meso-substituents have been synthesized and characterized. Coordination [Ru(bpy)2Cl]+ complexes to the pyridyl N-atoms has resulted in a series of BODIPY-Ru(II) complexes, Ru-1, Ru-2, and Ru-3. The spectroscopic and electrochemical properties of the BODIPY dyes and their Ru(II) analogs have been characterized. The electronic spectra of the dyes and dye-complexes reveal the intense absorption typical of the (pi pi*) transitions localized on the BODIPY core. The extended aromatic groups of dye 3 and its analog Ru-3 exhibit a 100 nm bathochromic shift in the BODIPY (pi pi*) transition. Additional metal-centered charge transfer transitions associated with the [Ru(bpy)2Cl]+ moieties are observed at higher energy compared to the BODIPY transitions. Extended DFT calculations of dyes 1 and 2 and their Ru(II) analogues Ru-1 and Ru-2 are in agreement to the experimental data. All three of the BODIPY-Ru(II) complexes exhibit significant singlet oxygen generation determined by the use of a singlet oxygen trap in acetonitrile solutions. Photo-reactions of the complexes in buffered aqueous solutions containing circular plasmid DNA (cpDNA) indicate that complexes Ru-1 and Ru-2 convert the cpDNA to its nicked form within minutes of irradiation. The Ru-3 complexes generates enough singlet oxygen to begin the photo-nicking of cpDNA but complete nicking of all cpDNA was not observed. This is most likely due to light induced decomposition of Ru-3 to its constituents; thereby, preventing further generation of singlet oxygen.