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It was proposed that Ru(II)[(1,10-phenanthroline)2dipyrido[3,2-a:2',3'-c]phenazine ([Ru(phen)2DPPZ]2+) complexes and 4',6-diamidino-2-phenylindole (DAPI) simultaneously bind to poly[d(A-T)2] (Biophysics. J. 2003, 85, 3865). Fšrster type resonance energy transfer from excited DAPI to [Ru(phen)2DPPZ]2+ complexes was observed. In this study, we synthesized - and -[Ru(phenanthroline)2dipyrido[3,2-a:2’,3’-c]6-azaphenazine] ([Ru(phen)2DPAPZ]2+) at which the DNA intercalating ligand DPPZ was replaced and we studied its binding properties to poly[d(A-T)2] in the presence and absence of DAPI using polarized spectroscopy and fluorescence techniques. All the spectroscopic properties of the [Ru(phen)2DPAPZ]2+-poly[d(A-T)2] complex were the same in the presence and absence of DAPI that blocks the minor groove of polynucleotide, suggesting both - and -[Ru(phen)2DPAPZ]2+ complexes are located at the major groove of poly[d(A-T)2]. On the other hand, in contrast with [Ru(phen)2DPPZ]2+, both - and -[Ru(phen)2DPAPZ]2+ exhibited almost twice the efficiency in the fluorescence quenching of DAPI that binds at the minor groove of poly[d(A-T)2]. This observation indicates that the efficiency of the Fšrster type resonance energy transfer can be controlled by a small change in the chemical structure of the intercalated ligand.