Red-Emitting [Ru(bpy)2(N-N)]2+ Photosensitizers: Emission from a Ruthenium(II) to 2,2′-Bipyridine 3MLCT State in the Presence of Neutral Ancillary “Super Donor” Ligands

A series of complexes containing bis(2,2′-bipyridine)ruthenium(II) and neutral ancilliary “super donor” ligands were synthesized and characterized. Their structural, electrochemical, and photophysical properties were studied and compared to those of tris(2,2′-bipyridine)ruthenium(II) and some reference compounds. Their properties were also modeled by density functional theory calculations, and trends were found vs the nature of the basicity of the heterocycle attached to the saturated aliphatic guanidium moiety

Red-Emitting [Ru(bpy)₂(N-N)]²⁺ Photosensitizers: Emission from a Ruthenium(II) to 2,2′-Bipyridine ³MLCT State in the Presence of Neutral Ancillary “Super Donor” Ligands

The synthesis and characterization of a novel family of [Ru^II(bpy)₂(N-N)]­(PF₆)₂ (bpy = 2,2′-bipyridine) complexes are reported, where N-N = pyridine/pyrimidine/pyrazine functionalized in different positions with the electron-donating bicyclic hexahydropyrimidopyrimidine (hpp) unit. A series of bidentate ligands <b>1a</b>–<b>5a</b> were synthesized in good to high yields (55–96%). The corresponding complexes <b>1b</b>, <b>2b</b>, and <b>5b</b> were prepared in <i>n</i>-butanol, while complexes <b>3b</b> and <b>4b</b> were prepared in a mixture of <i>n</i>-butanol and water (1/1, v/v) in modest to good yields (23–76%). Both ligand and complex structures were fully characterized by a variety of techniques, including X-ray crystallography. In cyclic voltammetric studies, all the complexes exhibit a Ru^III/II couple, which is ∼500 mV less positive than the Ru^III/II couple in Ru­(bpy)₃²⁺. The ¹MLCT and ³MLCT states of all of the complexes (530–560 nm/732–745 nm) are shifted bathochromically in comparison to those of Ru­(bpy)₃²⁺ (450 nm/620 nm). These values are in good agreement with DFT and TD-DFT calculations