Ruthenium(II)-Cored Polythiophene Dendrimers

We report the synthesis and characterization of ruthenium(II)-cored polythiophene dendrimers. Four new redox-active ruthenium(II) pyridine oligothiophene dendritic complexes that fluoresce in the near-infrared region have been synthesized, and their absorption spectra, fluorescence properties, and redox behavior have been investigated. The dendritic ligands phen3T and phen7T containing 1,10-phenanthroline as chelating sites and two oligothiophene dendrons (3T6COMe and 7T6COMe) have been synthesized and employed. The metal-polythiophene dendrimers investigated here are [Ru(bpy)(2)(phen3T)](2+), [Ru(bpy)(2)(phen7T)](2+), [Ru(phen3T)(3)](2+), and [Ru(phen7T)(3)](2+). Upon addition of acid, the charge transfer absorption bands of free dendritic ligands are significantly red-shifted and the fluorescence is greatly quenched. The Ru(II) polythiophene dendrimers exhibit very strong metal-to-ligand charge transfer (MLCT) absorption and enhanced absorption in the UV region and can be regarded as better light-harvesting species. The MLCT emission is extraordinarily red-shifted (similar to 165 nm) because of their planar excited states. The core of the dendrimers shows an electrochemical behavior typical of encapsulated metal electroactive units.