Photophysical Properties of Tetracationic Ruthenium Complexes and Their Ter-Ionic Assemblies with Chloride

The synthesis of seven ruthenium(II) polypyridyl complexes bearing one dicationic bis-4,4'-(trimethylaminomethyl)-2,2'-bipyridine (tmam) ligand is reported. The ancillary ligands of each complex were 2,2'-bipyrazine (bpz), 2,2'-bipyridine (bpy), 4,4'-tert-butyl-2,2'-bipyridine (dtb), 4,4'-dimethyl-2,2'-bipyridine (4,4'-dmb), 5,5'-dimethyl-2,2'-bipyridine (5,5'-dmb), 4,4'-nonyl-2,2'-bipyridine (nonyl), and 4,4'methoxy-2,2'-bipyridine (MeO). The metal-to-ligand charge transfer excited state was localized on the tmam ligand in all instances with the exception of [Ru(bpz)(2)(tmam)](4+), where it was localized on the bpz ligand. All [PF6](-) complexes were shown to form strong ion pairs with chloride in a Ru/Cl 1:2 stoichiometry in acetone, as evidenced by H-1 NMR and UV-visible titrations. With the exception of [Ru(bpz)(2)(tmam)](4+), ion pairing with chloride anions resulted in were similar to 25% longer-lived and with an similar to 50% increase in the photoluminescence quantum yields compared [PF6](-) ion pairs. It was shown that the quantum yield enhancements originated from a decreased nonradiative rate constant and an increased radiative rate constant. [Ru(bpy)(2)(tmam)](4+) showed curious excited state quenching behavior at higher equivalents of chloride, the origin of which is not understood.