Time-resolved and steady-state luminescence and transient resonance Raman measurements have been carried out on the complex [Ru(phen)(2)dppz](2+) (I) in the presence of single-stranded (ss) DNA that is either covalently attached to or mixed in 1:I ratio with the complex. The well-known enhancement of luminescence (the "light-switch" effect) exhibited by (1) when intercalated to double-stranded DNA is also observed in the presence of the single-stranded material, under conditions of covalent attachment or simple mixing. The evidence from both the luminescence and the transient Raman studies suggests that the enhancement need not necessarily reflect deep intercalation of the dppz ligand between the bases of the ss material.