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)](PF6)(2), where L is a 2-(2'-pyridyl)quinoline or 2-(2'-pyridyl)benzo[g]quinoline derivative, was investigated in acetonitrile solutions and ethanol-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 transient absorption spectrum with a decay rate constant approximately 30 times less than the luminescence decay rate constant, indicating the existence of two nonequilibrated excited states in the complex. Comparison 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 single MLCT excited state.