Laser flash-photolysis of methylene blue solutions

1979 ◽  
Vol 44 (7) ◽  
pp. 2015-2023 ◽  
Author(s):  
Viktor Řehák ◽  
Jaroslav Poskočil
Keyword(s):  
Methylene Blue ◽  
Electron Transfer ◽  
Energy Transfer ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Kinetic Measurements ◽  
Methanolic Solution ◽  
Triplet Excimer

Besides population and relaxation of T1 state of methylene blue in methanolic solution it has been possible to observe increase and decomposition of a transient with longer lifetime which is probably a triplet excimer of the dyestuff. Kinetic measurements have enabled to determine the lifetime of the T1 excimer, rate constants of energy-transfer to oxygen and electron-transfer from pyrrolidine to T1 of the dyestuff.

Photochemical Electron Transfer in the System Polypyrrole-Methylene Blue

1994 ◽  
Vol 47 (6) ◽  
pp. 1163 ◽  
Author(s):  
D Matthews ◽  
A Altus ◽  
A Hope
Keyword(s):  
Methylene Blue ◽  
Electron Transfer ◽  
Absorption Spectrum ◽  
Absorption Spectra ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Vitamin K1 ◽  
Photochemical Reduction ◽  
Long Chain

Methylene Blue incorporated into colloidal oxidized polypyrrole was investigated by absorption spectroscopy and laser flash photolysis. The absorption spectra of Methylene Blue and polypyrrole were unaffected by incorporation. Flash photolysis transients of Methylene Blue and triplet Methylene Blue in ethanol were affected by 1,4-benzoquinone and 1,4-benzoquinol but not by the long-chain naphthoquinone Vitamin K1. Incorporation of Methylene Blue in polypyrrole produced distinct changes in the flash photolysis transients of Methylene Blue and triplet Methylene Blue. Very long-lived transients, with lifetimes of the order of 10 ms, were observed. These effects were accompanied by long-lived changes in the absorption spectrum of Methylene Blue. The transients were modified by the addition of 1,4-benzoquinone but not 1,4-benzoquinol. The results indicate photochemical reduction of oxidized polypyrrole by triplet Methylene Blue with the production of stable long-lived species capable of reducing 1,4-benzoquinone.

Diazonium salts in photochemistry. I. Quenching of triplet photosensitizers

1982 ◽  
Vol 60 (17) ◽  
pp. 2286-2291 ◽  
Author(s):  
J. C. Scaiano ◽  
Nguyen Kim-Thuan
Keyword(s):  
Electron Transfer ◽  
Energy Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Diazonium Salt ◽  
Laser Flash ◽  
High Energy ◽  
Diazonium Salts ◽  
Transfer Mechanisms ◽  
Degree Of Charge Transfer

Aromatic diazonium tetrafluoroborates have been shown to be excellent triplet quenchers. Typical rate constants obtained using laser flash photolysis are in the 1–10 × 109 M−1 s−1 range in acetonitrile at 300 K. With most sensitizers the interaction leads to the dediazoniation reaction, via either energy transfer or electron transfer mechanisms. In the case of anthracene, where the rate constant for benzenediazonium tetrafluoroborate is (5.4 ± 0.3) × 109 M−1 s−1, the reaction involves the transfer of an electron, leading to the formation of anthracene radical-cation, which has been characterized by absorption spectroscopy. High energy sensitizers, such as benzophenone, are believed to lead to aryl cations and nitrogen; the process may involve some degree of charge transfer, since it is somewhat faster when electron donating substituents are present in the diazonium salt.

Photochemical Electron Transfer Between Methylene Blue and Quinones

1994 ◽  
Vol 47 (2) ◽  
pp. 209 ◽  
Author(s):  
M Misran ◽  
D Matthews ◽  
P Valente ◽  
A Hope
Keyword(s):  
Methylene Blue ◽  
Electron Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Lipid Vesicles ◽  
Laser Flash ◽  
Electron Transfer Reaction ◽  
Vitamin K1 ◽  
Photochemical Oxidant ◽  
Back Electron Transfer

Methylene Blue is a well known photochemical oxidant. In this paper we present results of cyclic voltammetry and laser flash photolysis experiments which demonstrate that Methylene Blue may function also as a photochemical reductant. Laser flash photolysis studies of Methylene Blue were carried out in aqueous solution at pH 10, in ethanol and in aqueous dispersions of lipid vesicles in the presence of benzoquinol , benzoquinone and the long-chain naphthoquinone Vitamin K1. Both the quinones and the quinol affected the transient of the decay of triplet Methylene Blue to its ground electronic state. The transients were biphasic and characteristic of an initial electron transfer reaction between triplet Methylene Blue and the quinone or quinol , followed by back electron transfer between the products. For Vitamin K1 and Methylene Blue in ethanol the back electron transfer was very slow (lifetime about 4 ms). This slow back electron transfer is favourable to the use of this system for energy storage via photosynthetic solar energy conversion.

Laser flash photolysis studies of 2,4,6-trialkylphenyl ketones

1989 ◽  
Vol 67 (3) ◽  
pp. 473-480 ◽  
Author(s):  
B. Guerin ◽  
L. J. Johnston
Keyword(s):  
Energy Transfer ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Hydrogen Donor ◽  
Quenching Rate ◽  
Phenyl Ketone

2,4,6-Triisopropylbenzophenone (3), 2,4,6–trimethylbenzophenone (4), and 2,4,6-trimethylacetophenone (5) have been examined by laser flash photolysis. Relatively long-lived triplets compared to similar mono-alkyl substituted ketones have been observed for each (280 ns, >2 μs and 220 ns in acetronitrile for 3, 4 and 5, respectively). Photoenol intermediates with λmax 360 nm and 380 nm were also observed from ketones 3 and 5, respectively. Ketone 3 yielded a mixture of approximately equal amounts of Z and E enols in hexane. The Z enol had a lifetime of ~4 μs while the E enol did not decay appreciably during 100 μs. Biradical intermediates were not observed from any of the three ketones. Quenching rate constants for several energy transfer and hydrogen donor substrates are reported. For example, ketones 3 and 4 react with 1,4-cyclohexadiene with rate constants of 2.8 × 107 and 3.7 × 107 M−1 s−1, respectively, to yield ketyl radicals with λmax ~480 nm. Keywords: photoenolization, trialkyl phenyl ketone, flash photolysis, triplets.

Singlet Methylene Removal Rate Constants from the (0,1,0) Vibrational Level: Enhancement via Complex-Mediated Vibrational Relaxation

2001 ◽  
Vol 215 (6) ◽  
Author(s):  
M.A. Buntine ◽  
G.J. Gutsche ◽  
W.S. Staker ◽  
M.W. Heaven ◽  
K.D. King ◽  
...  
Keyword(s):  
Vibrational Level ◽  
Rate Constants ◽  
Vibrational Relaxation ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Removal Rate ◽  
Laser Flash ◽  
Laser Absorption ◽  
Photolysis Laser ◽  
Singlet Methylene

The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene,

Electron transfer sensitized photolysis of 'onium salts

1988 ◽  
Vol 66 (2) ◽  
pp. 319-324 ◽  
Author(s):  
R. J. DeVoe ◽  
M. R. V. Sahyun ◽  
Einhard Schmidt ◽  
N. Serpone ◽  
D. K. Sharma
Keyword(s):  
Electron Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Quantitative Model ◽  
Intersystem Crossing ◽  
Single Electron Transfer ◽  
Onium Salts ◽  
Encounter Complex ◽  
Back Electron Transfer

We have studied the anthracene-sensitized photolyses of both diphenyliodonium and triphenylsulphonium salts in solution using both steady-state and laser flash photolysis techniques. Photoproducts, namely, phenylated anthracenes along with iodobenzene or diphenylsulphide, respectively, are obtained from both salts with quantum efficiencies of ca. 0.1 at 375 nm. We infer the intermediacy of diphenyliodo and triphenylsulphur radicals formed by single electron transfer from the singlet-excited anthracene. We have developed a quantitative model of this chemistry, and identify the principal sources of inefficiency as back electron transfer, which occurs at nearly the theoretically limiting rate, intersystem crossing from the initially formed sensitizer–'onium salt encounter complex, and in-cage radical recombination.

Laser flash photolysis studies of intramolecular electron transfer in milk xanthine oxidase

Biochemistry ◽  
1983 ◽  
Vol 22 (23) ◽  
pp. 5270-5279 ◽  
Author(s):  
Anjan Bhattacharyya ◽  
Gordon Tollin ◽  
Michael Davis ◽  
Dale E. Edmondson
Keyword(s):  
Electron Transfer ◽  
Xanthine Oxidase ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Intramolecular Electron Transfer
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