67005-45-2Relevant articles and documents
The Two-electron Oxidation of Methyl Viologen. Detection and Analysis of Two Fluorescing Products
Bahnemann, Detlef W.,Fischer, Christian-Herbert,Janata, Eberhard,Henglein, Arnim
, p. 2559 - 2572 (1987)
The oxidation of methyl viologen, 1,1'-dimethyl-4,4'-bipyridylium chloride (MV2+), in aqueous solution has been carried out γ-radiolytically and photocatalytically (in the presence of colloidal titanium dioxide).Two strongly fluorescing products have been observed, separated and identified: the 1',2'-dihydro-1,1'-dimethyl-2'-oxo-4,4'-bipyridylium cation maxfl(H2O) = 516 nm> and the 3,4-dihydro-1,1'-dimethyl-3-oxo-4,4'-bipyridylium cation maxfl(H2O) = 528 nm>.Both compounds exhibit characteristic u.v.-visible absorption spectra in aqueous solution with maxima at 222, 260 and 347 nm (ε = 14800, 20200 and 2400 dm3 mol-1 cm-1) or 236, 260 (shoulder) and 390 nm (ε = 12000, 5800 and 3700 dm3 mol-1 cm-1) for the 2-one or 3-one, respectively.Their relative abundance in the radiolysis experiments is strongly dependent on the absence or presence of secondary oxidants, e.g. dioxygen and ferric ions.The overall low G-values in the radiation chemical studies max(2-one) = 0.04, Gmax(3-one) = 0.11> indicates the formation of other as yet unidentified oxidation products.Comparatively high quantum yields are observed for both products upon ultra-bandgap irradiation of aqueous colloidal suspensions of TiO2, suggesting a simultaneous or consecutive two-hole transfer mechanism rather than a homogeneous free radical pathway is involved.Probable mechanisms of the .OH-induced oxidation of methyl viologen are discussed as well as the possible implication of these results on the use of MV2+ as an electron relay in solar energy devices.
