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

Abstract

Two new π‐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(dπ) to ligand(π*) 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 ππ* transition of the BDP‐core is observed. The less stable bis‐RuII BDP complex from the phenanthro‐fused dipyrrin was also synthesized giving the typical spectra associated with RuII‐phenanthroline complexes in addition an intense absorption at 618 nm from ππ* 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)2phen 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‐RuII‐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‐RuII‐BDP complex showing greater photoreactivity.