COEXISTENCE OF LIGAND LOCALIZED AND MLCT EXCITED-STATES IN A 2-(2'-PYRIDYL)BENZO[G]QUINOLINE COMPLEX OF RUTHENIUM(II)

The photophysical behavior of complexes of the type [(bpy)(2)Ru(L)](PF 6)(2), where L is a 2-(2'-pyridyl)quinoline or 2-(2'-pyridyl)benzo[g]q uinoline derivative, was investigated in acetonitrile solutions and et hanol-methanol glasses. The luminescence from each complex originates from a metal-to-ligand charge transfer excited state and the energy of the emission maxima correlate with other reported quinoline complexes of Ru(II). The 2-(2'-pyridyl)benzo[g]quinoline complex has a unique t ransient absorption spectrum with a decay rate constant approximately 30 times less than the luminescence decay rate constant, indicating th e existence of two nonequilibrated excited states in the complex. Comp arison with other related complexes suggests the long-lived transient absorption may be due to a ligand localized (pi --> pi) excited state . The pyridylquinoline complex exhibits behavior characteristic of a s ingle MLCT excited state.