Tuning and Switching MLCT Phosphorescence of [Ru(bpy)3]2+ Complexes with Triarylboranes and Anions

Four new Ru(II) complexes, [Ru(bpy)(2)(4,4'-BP2bpy)][PF6](2) (1), [Ru(t-Bu-bpy)(2)(4,4'-BP2bpy)][PF6](2) (2), [Ru(bpy)(2)(5,5'-BP2bpy)][PF6](2) (3), and [Ru(t-Bu-bpy)(2)(5,5'-BP2bpy)][PF6](2) (4) have been synthesized (where 4,4'-BP2bpy = 4,4'-bis(BMes(2)phenyl)-2,2'-bpy; 5,5'-BP2bpy = 5,5'-bis(BMes(2)phenyl)-2,2'-bpy (4,4'-BP2bpy); and t-Bu-bpy = 4,4'-bis(t-butyl)-2,2'-bipyridine). These new complexes have been fully characterized. The crystal structures of 3 and 4 were determined by single-crystal X-ray diffraction analyses. All four complexes display distinct metal-to-ligand charge transfer (MLCT) phosphorescence that has a similar quantum efficiency as that of [Ru(bpy)(3)][PF6](2) under air, but is at a much lower energy. The MLCT phosphorescence of these complexes has been found to be highly sensitive toward anions such as fluoride and cyanide, which switch the MLCT band to higher energy when added. The triarylboron groups in these compounds not only introduce this color switching mechanism, but also play a key role in the phosphorescence color of the complexes.