Ruthenium(II) Polypyridyl Complexes Coordinated Directly to the Pyrrole Backbone of π-Extended Boron Dipyrromethene (Bodipy) Dyes: Synthesis, Characterization, and Spectroscopic and Electrochemical Properties.

Abstract

A series of new Bodipy dyes incorporating the π-extended isoquino[5,6-c]pyrrole have been synthesized and characterized. The dyes display intense Bodipy (π-π*) transitions and emissions with high quantum efficiencies. Spectroscopic, electrochemical, and theoretical calculations are used to give insight into the frontier orbitals. Coordination of {Ru(bpy)2Cl}+ subunits to the peripheral isoquinol nitrogen atoms of the Bodipy dyes leads to three new bis-Ru(II)-polypyridyl-Bodipy complexes with the Ru(II) centers in direct contact with the dipyrrin core. Spectroscopic studies of the complexes reveal the traditional metal to ligand charge transfer (MLCT) transitions associated with Ru(dπ) to bpy(π*) transitions. However, a more intense transition above 600 nm is also observed. This transition is independent of the meso-substituents of the dipyrrin and is shifted to lower energy by as much as 25 nm compared to that of the Bodipy dyes without the Ru(II) subunits. Spectroscopic, electrochemical, and spectroelectrochemical studies suggest that the Bodipy π-orbitals are destabilized by coordination of the Ru(II) moieties. All three Ru2-Bodipy complexes show the ability to generate singlet oxygen when irradiated within the photodynamic therapy window (600-850 nm) as evidenced by singlet oxygen trapping experiments.