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Ruthenium(II) polypyridyl complexes (RPCs) that emit from triplet metal-to-ligand charge transfer (MLCT) states find a wide variety of uses ranging from luminophores to potential anti-cancer or anti-bacterial therapeutics. Herein we describe a greener, microwave-assisted synthetic pathway for the preparation of homoleptic [Ru(N^N) 3 ] 2+ and bis-heteroleptic [Ru(N^N) 2 (N'^N')] 2+ type complexes. This employs the bio-renewable solvent Cyrene™, dihydrolevoglucosenone, as a green alternative to N , N '-dimethylformamide (DMF) in the synthesis of Ru(N^N) 2 Cl 2 intermediate complexes, obtaining comparable yields for N^N = 2,2'-bipyridine, 1,10-phenanthroline and methylated derivatives. Employing these intermediates, a range of RPCs were prepared and we verify that the ubiquitous luminophore [Ru(bpy) 3 ] 2+ (bpy = 2,2'-bipyridine) can be prepared by this two-step green pathway where it is virtually indistinguishable from a commercial reference. Furthermore, the novel complexes [Ru(bpy) 2 (10,11-dmdppz)] 2+ (10,11-dmdppz = 10,11-dimethyl-dipyridophenazine) and [Ru(5,5'-dmbpy) 2 (10,11-dmdppz)] 2+ (5,5'-dmbpy = 5,5'-dimethyl-bpy) intercalate duplex DNA with high affinity (DNA binding constants, K b = 5.7 × 10 7 and 1.0 × 10 7 M -1 , respectively) and function as plasma membrane and nuclear DNA dyes for confocal and STED microscopies courtesy of their long-lived MLCT luminescence.

Ruthenium(II) polypyridyl complexes (RPCs) that emit from metal-to-ligand charge transfer (MLCT) states have been developed as DNA probes and are being examined as potential anticancer agents. Here, we report that MLCT-emissive RPCs that bind DNA undergo Förster resonance energy transfer (FRET) with Cy5.5-labeled DNA, forming mega-Stokes shift FRET pairs. Based on this discovery, we developed a simple and rapid FRET binding assay to examine DNA-binding interactions of RPCs with diverse photophysical properties, including non-"light switch" complexes [Ru(dppz) 2 (5,5'dmb)] 2+ and [Ru(PIP) 2 (5,5'dmb)] 2+ (dppz = dipyridophenazine, 5,5'dmb = 5,5'-dimethyl-2,2'-bipyridine, PIP = 2-phenyl-imidazo[4,5- f ][1,10]phenanthroline). Binding affinities toward duplex, G-quadruplex, three-way junction, and mismatch DNA were determined, and derived FRET donor-acceptor proximities provide information on potential binding sites. Molecules characterized by this method demonstrate encouraging anticancer properties, including synergy with the PARP inhibitor Olaparib, and mechanistic studies indicate that [Ru(PIP) 2 (5,5'dmb)] 2+ acts to block DNA replication fork progression.