Reactivity of Organic Dye Triplet States in Electron Transfer Processes

Vogelmann, Ekehardt; Schreiner, S.; Rauscher, Wolfgang; Kramer, Horst E. A.

doi:10.1524/zpch.1976.101.1-6.321

Cited by 76 publications

(19 citation statements)

References 26 publications

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“…(12) In the case of 'double le-transfer', the radical recombination ought to be much faster than HFl dismutation, while the latter could only occur with concomitant formation of radical dimers R2, which have never been observed. 3Flzx + RH -+ HFl + R * + RFl,,dH.…”

Section: Flush Photolysis In the Presence Of'bh3cnmentioning

confidence: 99%

“…The flash apparatus described by Vogelmann et al [12] was used. The input energy of the flash was 600 J (half duration about 8 ps).…”

Section: Flash Photolysismentioning

confidence: 99%

“…In other words, the whole radical yield observed in flavin-sensitized photo-dehydrogenation reactions can be reconciled as being due to side effects, while the 'double le-transfer' [Eqn (12)], postulated extensively in the earlier literature, remains less relevant, if at all, and negligible at least in the present case B. (12) In the case of 'double le-transfer', the radical recombination ought to be much faster than HFl dismutation, while the latter could only occur with concomitant formation of radical dimers R2, which have never been observed.…”

Section: Flush Photolysis In the Presence Of'bh3cnmentioning

confidence: 99%

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Distinction of 2e- and le- Reduction Modes of the Flavin Chromophore as Studied by Flash Photolysis

Hemmerich

Knappe

Kramer³

et al. 1980

Eur J Biochem

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Evidence is given for the fact that the excited flavin triplet (3F10*x) exhibits competitive le-and 2e-transfer chemistry, depending on the nature of the photosubstrate. As an 'external' photoreductant, the 2e-donor borohydride has been investigated. Borohydride is found to compete effectively with the 'internal' 1 e-donors, namely excess starting flavin in the ground state (Flax) and, as primary product, (alky1)dihydroflavin (RFl,,dH). It will be shown that some of the flavin radicals, observed by earlier authors in the reaction of 3Fl& with CH or C -COO-substrates or in the autophotolytic side-chain cleavage of riboflavin, are due to the dye-dye reaction (I) :(1) H i In contrast flavin photoreduction by borohydride or hydrocarbon substrates need not involve radicals, but may in fact be a hydride or 'carbanion-plus-proton' addition towards the highly polar and considerably basic (pK = 4.4) acceptor triplet (cf. reaction 11) RCOO-The products are much more photoreactive than the starting substrates, which leads to the secondary photocomproportionation (111) : 3Fl,*, + R-Fl,,dH + HFl + RFl, (R = alkyl or H). (111) This latter reaction is the second source of radicals in the system. This (cf. 11) 'photohydrogenation' of flavin is mechanistically related to the biological reduction of flavin by CH substrates.The photochemistry of flavins is in fact older than the corresponding ground-state chemistry and even biochemistry, since the side-chain photolysis of vitamin Bz was the first flavin reaction to be discovered [l]. The very complex course of this reaction, yielding lumiflavin at alkaline pH and lumichrome at neutrality, is still not completely resolved [2] (and references therein). This is largely due to a common mistake of insisting that such reactions must involve radical Dedicated to Professor Hellmut Bredereck, Universitat Stuttgart, on his 75th birthday.Abbreviations. Fl,,, flavoquinone, flavin; 3Fl,*,, excited flavin triplet; HFI Fl-, acidic and basic flavosemiquinone; Fl', oxidized flavin radical; HZFlred, flavohydroquinone, 1,5-dihydroflavin.

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Section: Flush Photolysis In the Presence Of'bh3cnmentioning

confidence: 99%

“…The flash apparatus described by Vogelmann et al [12] was used. The input energy of the flash was 600 J (half duration about 8 ps).…”

Section: Flash Photolysismentioning

confidence: 99%

Section: Flush Photolysis In the Presence Of'bh3cnmentioning

confidence: 99%

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Distinction of 2e- and le- Reduction Modes of the Flavin Chromophore as Studied by Flash Photolysis

Hemmerich

Knappe

Kramer³

et al. 1980

Eur J Biochem

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“…Using, e.g., ferrous 13, 27). Applying allythiourea (8,28) or Paraions in acid solution, the process can be summar-phenylendiamine (9) concentration of the electron donor can influence k3 = 6 x lo7 dm3 mol-I s-' (25) the yield of semiquinone (12,15,29,30 A direct formation of semiquinone, avoiding all above mentioned factors can be achieved by reaction of thionine with H-atoms. The pulse radiolysis technique offers this possibility.…”

Section: Introductionmentioning

confidence: 99%

Attack of H-atoms on aqueous thionine studied by pulse radiolysis

Solar¹,

Getoff²,

Solar³

et al. 1981

Can. J. Chem.

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SONIA SOLAR, NIKOLA GETOFF, WOLFGANG SOLAR, and FRANZ MARK. Can. J. Chem. 59,2719Chem. 59, (1981.The reaction mechanism of the H-attack on thionine (TH+) in aqueous solutions (5 X to 2 X mol dm+ TH+; 2 x mol dm-3 r-butanol, pH I and 4) was investigated by pulse radiolysis in combination with simulation by computation. Applying a least-squares fitting procedure it was possible to state that at pH 1,89.5% of the H-atoms react with TH+, k = (8.5 f 0.3) x lo9 dm3 mol-I s-I, to form semiquinone ('TH3Z+, Amax = 390nm, E,,, = 685 f 20 m2 mol-I; &770 = 720 mZ mol-' and Amax = 790nm, E, , , = 775 f 20mZ mol-I), which dismutates to TH+ and leucodye with 2k = (2.4 f 0.1) X lo9 dm3 mol-I s-I. In addition to this a second H-attack (10.5% H) occurs on the ring carbon of the dye with k = (1.0 f 0.1) x lo9 dm3 mol-' s-l, resulting in the production of H-adducts. These results are of interest for photogalvanic cells using thionine as a sensitizer., SONIA SOLAR, NIKOLA GETOFF, WOLFGANG SOLAR et FRANZ MARK. Can. J. Chem. 59,2719Chem. 59, (1981.Utilisant la radiolyse par pulsation combinee avec une simulation obtenue par le calcul, on a ttudie le mecanisme de la reaction 1 d'attaque du H sur la thionine (TH+) dans des solutions aqueuses (5 x a 2 x mol dm-' TH+; 2 x mol d m 3 rerr-butanol,

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“…Other approaches have used the Marcus theory of outer-sphere electron transfer reactions (40) which predicts an inverted region where ki drops from the plateau value when AG^ becomes very negative. "Vestiges" of the inverted region have been found in the quenching of *Ru(bpy)3 (41) but not in the quenching of triplet thionine (42). Irrespective of the intricacies of these theories, the analysis performed above shows that for short-lived excited states (T* R ^ 10~6 s ) t reaction with kl at or near the diffusioncontrol led limit is necessary for efficient conversion of *R to separated charge carriers.…”

Section: Formation Of Separated Charge Carriersmentioning

confidence: 93%

Photochemical Determinants of the Efficiency of Photogalvanic Conversion of Solar Energy

Hoffman

Lichtin

1979

Solar Energy

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A photogalvanic cell is a battery in which the cell solution absorbs light directly to generate species which, upon back reaction through an external circuit with the aid of suitable electrodes, produces electric power; photoactivation of the electrodes is 'not involved. The charge-carrying species have storage capacity if they are long-lived and can be prevented from engaging in degradativc back reactions in bulk solution. The efficiency of a photogalvanic cell for the conversion of photon energy into electrical energy is determined by photochemical and electrochemical factors. Among the latter are the choice of electrode materials and the kinetics of electron transfer at the heterogeneous surfaces. In this paper we examine '"the photochemical determinants of the efficiency of photogalvanic eel] operation: the absorption spectral characteristics of the cell solution, the efficiency of formation of separated charge carriers, and the lifetimes of the carriers toward back electron transfer. Modulation of bulk solution dynamics can be achieved by variation of the solution medium. The photochemical determinants are discussed with particular reference to the use of thionine or Ru(bpy)2+ as the light absorbing species.

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Reactivity of Organic Dye Triplet States in Electron Transfer Processes

Cited by 76 publications

References 26 publications

Distinction of 2e- and le- Reduction Modes of the Flavin Chromophore as Studied by Flash Photolysis

Distinction of 2e- and le- Reduction Modes of the Flavin Chromophore as Studied by Flash Photolysis

Attack of H-atoms on aqueous thionine studied by pulse radiolysis

Photochemical Determinants of the Efficiency of Photogalvanic Conversion of Solar Energy

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