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The Two-electron Oxidation of Methyl Viologen. Detection and Analysis of Two Fluorescing Products

DOI: 10.1039/f19878302559

Source and publish data:

Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases p. 2559 - 2572 (1987)

Update date:2022-08-05

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Authors:

Bahnemann, Detlef W.Bahnemann, Detlef W.

Fischer, Christian-HerbertFischer, Christian-Herbert

Janata, EberhardJanata, Eberhard

Henglein, ArnimHenglein, Arnim

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Article abstract of DOI:10.1039/f19878302559

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 <'2-one', λmaxfl(H2O) = 516 nm> and the 3,4-dihydro-1,1'-dimethyl-3-oxo-4,4'-bipyridylium cation <'3-one', λmaxfl(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<Φ(2-one) = 0.032, Φ(3-one) = 0.01>, 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.

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Product name:pyridinium, 4-(1,2-dihydro-1-methyl-2-oxo-4-pyridinyl)-1-methyl-, chloride (1:2)

Cas No:67005-45-2

67005-45-2

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