Bichromophoric Properties of Ruthenium(II) Polypyridyl Complexes Bridged by Boron Dipyrromethenes: Synthesis, Electrochemical, Spectroscopic, Computational Evaluation, and Plasmid DNA Photoreactions

Two new pi-extended dipyrrins containing isoquinolpyrrole and phenanthro-fused pyrrole have been synthesized by solvent free reactions with trifluoroacetic acid (TFA) as a catalyst. The boron-dipyrrin (BDP) of the isoquinolpyrrole was synthesized by standard procedures followed by synthesis of the bis-ruthenium(II) BDP analog. The spectroscopic properties of this complex were investigated, showing the typical intra-ligand charge transfer transitions (ILCT) along with the Ru(d pi) to ligand(pi*) metal to ligand charge transfer (MLCT) transitions. An intense transition at 608 nm with molar absorptivity greater than 100,000 m(-1) cm(-1) associated with the pi pi* transition of the BDP-core is observed. The less stable bis-Ru-II BDP complex from the phenanthro-fused dipyrrin was also synthesized giving the typical spectra associated with Ru-II-phenanthroline complexes in addition an intense absorption at 618 nm from pi pi* transition of the BDP-core. The spectroscopic properties of this complex were correlated to density functional theory (DFT) and time-dependent density functional theory (TDDFT) theoretical calculations. This complex shows interesting dual emission of both the Ru(bpy)(2)phen and the BDP-core components at 601 nm and 641 nm respectively upon excitation of the lower energy MLCT transition at 453 nm. In acetonitrile solutions both bis-Ru-II-BDP complexes generate significant singlet oxygen when irradiated with low energy light. In aqueous solutions both complexes are capable of photo-nicking plasmid DNA when irradiated within the photodynamic therapy (PDT) window with the phenanthrol-fused bis-Ru-II-BDP complex showing greater photoreactivity.