Probing the interaction of [Ru(phen)(2)(dppz)](2+) with single-stranded DNA - What degree of protection is required for operation of the "light-switch effect"?

Time-resolved and steady-state luminescence and transient resonance Raman m easurements 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 attac hed to or mixed in 1:I ratio with the complex. The well-known enhancement o f luminescence (the "light-switch" effect) exhibited by (1) when intercalat ed to double-stranded DNA is also observed in the presence of the single-st randed material, under conditions of covalent attachment or simple mixing. The evidence from both the luminescence and the transient Raman studies sug gests that the enhancement need not necessarily reflect deep intercalation of the dppz ligand between the bases of the ss material.