2,2 -bipyridyl quinones

The photostability of Os(II) bipyridyl complexes with covalently attached hydro quinone was investigated by Keyes and coworkers. In the complex [Os(bpy)2(bbhq)]+ (Scheme 1) the Os(II) center is coordinated to one ligand nitrogen and one of the oxygens of the central hydro quinone. The complex has an Os to bpy MLCT absorption with a maximum of 493 nm, but is non-luminescent. Photolysis in acetonitrile in the presence of excess Cl" did not yield any measurable photodegradation [32]. 

The luminescence spectra of all receptors in CH3CN were found to be dramatically affected by the addition of acetate or chloride. While compound 19 exhibits an emission decrease, the other receptors 17,18 and 20 show a remarkable intensity increase (up to 500%) with a slight concomitant blue shift of the emission maximum (660 nm for 17). The anion-induced enhancement of luminescence intensity in the case of 17 is clearly due to the decrease of the electron transfer between the ruthenium(II) bipyridyl centre and the quinone moieties. Alternatively, receptors bearing ruthenium or rhenium complexes on the upper rim were also described [20]. 

IR spectra, 712 magnetic properties, 710 synthesis, 709 quinones, 716 tertiary phosphines dinitrogen, 713 tris bipyridyl)... 

When a metal complex like osmium(II) fris(bipyridyl) or a metallocene, as in compound 3, is appended to the ligand, the MLCT excited state is quenched by energy transfer to the adjacent metal center. The rate of this quenching decreases as an anionic substrate binds between the two metal eomplexes. A similar switching mechanism is seen in the calix[4]diquinone-appended complex, 4. In this case, the fluorescence emission is quenched via an intramolecular electron transfer to the quinone. Anion binding between the Ru complex and the quinone blocks the quenching process, and the emission intensity is significantly recovered. 

A similar process mediated by a catecholato-bipyridyl (phenanthrolyl) Cu(II) complex (Scheme 8) was found to be oxygen-dependent in keeping with intra-complex dioxygen transfer 47). Once again, other mechanisms are possible. Oxygen could be reduced to hydroperoxide and react with the appropriate o-quinone outside the co-ordination sphere 48). The binuclear p-peroxo complex (8) could also be implicated and, if so, it would behave similarly to the catalytically active species encountered in other oxygen-dependent cuprous chloride/pyridine oxidations 49). 

The metallointercalator-DNA conjugates ([Ru ][9.10-phenanthrone quinone diimine]2[4-butyric acid-4 -methyl bipyridyl]-DNA, where DNA is a 20-mer oligonucleotide) attached to the 5 or 3 terminus, were synthesized and separated on a C g column (A = 260 nm or 390 run). A 50/50 water (50 mM armnoniinn acetate buffer at pH 6)/acetonitrile mobile phase generated baseline resolution and elution in 35 min [1198]. 

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