Synthesis, Characterization, and DNA Binding Properties of Ruthenium(II) Complexes Containing the Redox Active Ligand Benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine-11,16-quinone

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Abstract
Synthetic methods toward ruthenium(II) complexes incorporating the benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine-11,16-quinone ligand, qdppn, are reported. In several cases, it was found that complexes containing coordinated benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine, dppn, could be chemically or photochemically oxidized to their qdppn analogues. Since this method was not possible in all the cases, a new, higher yielding, convenient synthesis of qdppn was developed. The crystal structure of the complex [Ru(phen)2(qppn)](PF6)2 (phen = 1,10-phenanthroline) which was synthesized from free qdppn reveals that a combination of π–π stacking between coordinated phen and qdppn units, as well as anion-ligand hydrogen bonding, define large hexagonal channels which are occupied by anions and solvent molecules. Electrochemical and photophysical studies reveal that the new qdppn-based complexes are not luminescent and, in contrast to their dppn analogues, they are also poor singlet oxygen sensitizers. Time-resolved studies and density functional theory (DFT) calculations indicate that optical properties of the new complexes are due to a short-lived charge separated state involving the quinone moiety of qdppn. The DNA binding properties of the new complexes have also been investigated. It was found that they are intercalators, displaying binding affinities which are comparable to their dppn analogues.

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