ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
In the context of our studies on ruthenium(II) complexes containing polyazaheterocyclic ligands, we have determined the rate constants of quenching by molecular oxygen (kq) of the metal-to-ligand charge-transfer-excited state of a series of homoleptic [RuL3] complexes (where L stands for 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2′-bipyrazine (bpz), 4,7-diphenyl-1,10-phenanthroline (dip), diphenyl-1,10-phenanthroline-4,7-disulfonate (dpds), and 1, 10-phenanthroline-5-octadecanamide (poda)) in H2O and in MeOH. These compounds are singlet-oxygen (O2(1Δg)) sensitizers, and quantum yields of singlet-oxygen production (ΨΔ) in both solvents are also reported. Values of kq and ΨΔ depend on the nature of the ligand L and on the solvent, ΨΔ values showing a large range of variation (0.2 to 1.0). In MeOH, the only pathway for quenching of the excited [RuL3] complexes by molecular oxygen is energy transfer: the fraction of quenched excited states yielding singlet oxygen (ƒΔT) is unity for all compounds in the series investigated. Changing from MeOH to H2O has several remarkable effects: higher kq and lower ΨΔ values are observed; ƒΔT drops to ca. 0.5 except for [Ru(bpz)3]2+. In fact, [Ru(bpz)3]2+ is by far the weakest reductant in the series and behaves differently from the other complexes, with lowest kq and ΨΔ values and a ƒΔT equal to 1 in both solvents. Results are interpreted on the basis of the role played by charge-transfer interactions between the sensitizer excited state and molecular oxygen in the quenching mechanism. RuII Complexes based on the 4,7-diphenyl-1, 10-phenanthroline (dip) ligand are very efficient and stable singlet-oxygen sensitizers with ΨΔ values close to unity in air-saturated MeOH.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19960790428
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