Synthesis, Electrochemistry, and Excited-State Properties of Three Ru(II) Quaterpyridine Complexes

The complexes [Ru(qpy)LL'](2+) (qpy = 2,2':6',2 '':6 '',2 '''-quaterpyridine), with 1: L = acetonitrile, L' = chloride; 2: L = L' = acetonitrile; and 3: L L' = vinylpyridine, have been prepared from [Ru(qpy) (Cl)(2)]. Their absorption spectra in CH3CN exhibit broad metal-to-ligand charge transfer (MLCT) absorptions arising from overlapping (1)A(1) -> (MLCT)-M-1 transitions. Photoluminescence is not observed at room temperature, but all three are weakly emissive in 4:1 ethanol/methanol glasses at 77 K with broad, featureless emissions observed between 600 and 1000 nm consistent with MLCT phosphorescence. Cyclic voltammograms in CH3CN reveal the expected Rumiu redox couples. In 0.1 M trifinoroacetic acid (TFA), 1 and 2 undergo aquation to give [Ru-II(qpy)(OH2)(2)](2+), as evidenced by the appearance of waves for the couples [Ru-III(qpy)(OH2)(2)](3+)/[Ru-II(qpy)(OH2)(2)](2+), [Ru-IV(qpy)(O)(OH2](2+)/[Ru-III(qpy)(OH2)(2)](3+), and [Ru-VI(qpy)(O)(2)](2+)/[Ru-IV(qpy)(O)(OH2)(2)](2+) in cyclic voltammograms.