PHOTOCHEMICAL ELIMINATION OF SINGLET OXYGEN FROM OXODIPEROXO-MOLYBDENUM(VI) COMPLEXES WITH AROMATIC N,N'-CHELATE LIGANDS

The photolysis of the oxodiperoxo-molybdenum(VI) complexes of the type (L-L)MoO(O-2)(2) (L-L = 2-(1-alkyl-3-pyrazolyl)pyridine, alkyl = n-bu tyl 1a, n-octyl 1b, n-octadecyl 1c; L-L = 2-(3-n-octyl-2-imidazolyl) p yridine 2) leads to the elimination of molecular oxygen both in its si nglet and in its triplet state. Solutions of the diperoxo complexes co ntain two isomers A and B. The overall quantum yields of the photolysi s, (Q) over bar(Ph), and of the generation of singlet oxygen (O-1(2)), (Q) over bar(Delta), were measured in methylene chloride as a functio n of the irradiation wavelength. From the wavelength dependence of (Q) over bar(Ph) it can be deduced that the quantum yields of the photoly sis of the two isomers are not equal. Furthermore, for all diperoxo co mplexes fluorescence is observed, and for the complexes 1a, 1b, and 1c , additionally, phosphorescence is observed. The overall quantum yield s of the fluorescence, (Q) over bar(F), are in the range (1.5-8.0) x 1 0(-3).