Electron acceptor properties of excited trans-thioindigo

Memming, R.; Kobs, K.

doi:10.1021/j150619a016

Cited by 9 publications

(11 citation statements)

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“…No quenching by toluene ( E r = 1.97 V) has been observed, in contrast to the thioindigo compounds (22), the reduction potentials (-0.5 V) of which are slightly less negative than that of the indigo derivatives (-0.58 V).…”

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 80%

“…It is known that the isomerization of stilbenes results from a singlet excited state (10,16) and that for thioindigo derivatives, molecules which are closely related to the series studied here, it depends on the geometry of the starting material with the trans isomer undergoing a photoisomerization via the triplet excited state (17)(18)(19), while the reverse photochemical reaction occurs from the singlet state (20,21). When the c -, t isomerization of thioindigo derivatives was studied in a toluene-containing solution, the isomerization quantum yield was found to vary with the temperature and to reach a maximum value (ca.…”

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 90%

“…When the c -, t isomerization of thioindigo derivatives was studied in a toluene-containing solution, the isomerization quantum yield was found to vary with the temperature and to reach a maximum value (ca. 0.9) at 180 K; this effect could be rationalized (22) on the basis of the formation of an exciplex between the excited cis-indigos and toluene. The multiplicity of the excited state involved in the t -, c isomerization has been questioned by Haucke and Paetzold (20) who found that oxygen quenches this process, but not completely (about 90%); such a quenching was already described by Kirsch and Wyman (17).…”

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 93%

“…Thioindigo derivatives have been found to interact with hydroxyl compounds such as phenols (29) and alcohols (30); they have been reported also to behave like electron acceptors (22) in donor-acceptor interactions. This prompted us to investigate the effect of electron donors on the excited state of the indigo derivatives 1 t, 2t, and 3 t.…”

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 99%

“…If the quenching process occurs from an electron acceptordonor exchange, as is the case for the thioindigo derivatives (22), then the rate constant Kq should vary with the oxidation potential of the donor E r . According to the pioneering work of Leonhard and Weller (33), the rate constant K, for the fluorescence quenching process should increase with decreasing E r of the donor, until a plateau is reached when Kq is equal to the diffusion rate constant of the solvent (34,35).…”

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 99%

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Photoisomerization of N,N′-disubstituted indigos. A search for energy storage

Pouliquen¹,

Wintgens²,

Toscano³

et al. 1984

Can. J. Chem.

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The photochemical behaviour of N,N1-disubstituted indigo dyes has been investigated. The trans to cis and cis to trans photoisomerization quantum yields are found to be of the order of 0.25 or less (down to 0.03). These dyes, which fluoresce only weakly in solution and at room temperature, show a drastic increase in their fluorescence when inserted into a polymer matrix or at 77 K in butyronitrile glass. This has been interpreted in terms of the inhibition of formation of a twisted excited intermediate as well as of the rotation of the substituent on the nitrogen atom. An important electron transfer occurs from the singlet excited state when the indigo dyes are placed in the presence of electron-donating molecules. When irradiating with visible light, the photostationary state is always in favour of the trans isomers. This, and kinetic as well as thermodynamic considerations, excludes these compounds as candidates for solar energy storage.JOSEPH POULIQUEN, VERONIQUE WINTGENS, VICENTE TOSCANO, BRAHIM BEN JAAFAR, SADHANA TRIPATHI, JEAN KOSSANYI et PIERRE VALAT. Can. J. Chem. 62, 2478 (1984.Le comportement des indigos substituks 1-4 a kt6 examink. On trouve que les rendements quantiques de photoisomerisation sont faibles (de l'ordre de, ou infkrieurs 9, 0,20). Ces composks qui fluorescent faiblement en solution et B 20°C, prksentent une augmentation considkrable de leur fluorescence quand ils sont inclus dans un polymkre ou bien lorsque la tempkrature est abaisske B 77 K dans le butyronitrile. Ceci a kt6 interpret6 comme un empschement a la rotation autour de la double liaison centrale, et comme une gene i la rotation du substituant sur l'azote ainsi que de l'inversion de cet atome. L'irradiation en lumi2re blanche est toujours en faveur des isomkres trans. Ceci, ainsi que des considkrations cinktiques et thermodynamiques excluent ces composks pour le stockage de l'tnergie solaire. IntroductionIn the search for new sources of energy, photochemical transformations have been examined as a potential means of obtaining energy-rich stable products. Criteria for efficient photochemical conversion of solar energy are: absorption in the visible or near-ultraviolet region, high quantum efficiencies, large positive ground state enthalpies, and stable photoproducts. In addition, the reactant must be inexpensive and not dangerous.The importance of dyes has been widely recognized in different converting systems related to photobiology (1,2), photoelectrochemistry (3, 4), and photochemistry (5).Photochemical systems mostly involve (Fig. 1) absorption of visible light by a reagent R to produce a high energy content product P which can later release the stored energy while reverting to the starting material. Among the systems reported thus far, one finds intramolecular cycloadditions (the best system investigated seems to be the norbornadiene-quadricyclane one (6) which can store about 26 kcal/mol(7)) and valence isomerization (such as the photochemical transformation of 1-methyl 5-phenyl A-2 pyrazoline into 2-phenylcyclopropylazo...

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Section: A Excited State Involved In the Isomerizationmentioning

confidence: 80%

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 90%

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 93%

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 99%

Section: A Excited State Involved In the Isomerizationmentioning

confidence: 99%

See 3 more Smart Citations

Photoisomerization of N,N′-disubstituted indigos. A search for energy storage

Pouliquen¹,

Wintgens²,

Toscano³

et al. 1984

Can. J. Chem.

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A Proton NMR Study of the Dynamics of Ligand Exchange on Tetrakis(1,1,3,3‐Tetramethylurea)Beryllium(II) and its Dimethyl Sulphoxide Analogue

Lincoln

Tkaczuk

1981

Ber Bunsenges Phys Chem

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St. F. Lincoln and M. N. Tkaczuk: A Proton NMR Study of the Dynamics of Ligand Exchange etc. 433 proceeds with a quantum efficiency higher than 0.46. On the other hand, the quantum efficiency of RhB triplet formation is 0.006 in water (291. Hence, if process (9) is operative in cosensitization by Br-and C1-, these ions should enhance the RhB intersystem crossing by a factor larger than 80. This seems, by all means, improbable.Thus the origin for cosensitization by Br-and CI-ions should be sought in promotion of RhB adsorption t o the CdS surface (92). This type of mechanism has been put forth by Bode and Hauffe [9] for SCN-ion but not for halide ions. Although a quantitative agreement is not seen between the cosensitization ( Fig. 1) and adsorption promotion ( Fig. 3), this may again reflect the different surface conditions of CdS single crystal and powder.The above discussion could be rationalized with the redox level diagram illustrated in Fig. 4. Strong reducing agents such as HQ, I -, and Fe2+, with redox potentials negative of the RhB/RhBf couple, can regenerate RhB through process (8). Quenching of RhB fluorescence by all the additives employed is explained on account of the energetic correlation between the redox levels of these additives and that of the RhB*/RhB; couple. However, in the presence of a very fast process (7), a direct photoreduction of RhB is not possible at least by Br-and CI-ions. Figs. 1 and 2 show that H Q is more effective than I -, though the redox potential of the former lies at a somewhat positive value than the latter. This may have resulted from a kinetic factor in process (8), or from a difference in the reorganization energy [ 5 ] between H Q and I -.A 'H (90 MHz) NMR study of 1,1,3,3-tetramethylurea exchange on [Be(O= C(NMe2)2)4]2+ in the non-co-ordinating diluents CD3N02 and CD3CN shows that the exchange rate is independent of the free 1,1,3,3-tetramethylurea concentration. Typically k, (298.2 K) = 1.39 * 0.09 s-', AH' = 77.1 f 1.5 kJ mol-I, and AS' = 16.4 * 4.3 J K -' mol-' for a solution in which [Be(O=C(NMe2)2):+], [O=C(NMe2)2]free, and [CD3NOz] = 0.00743, 0.0334, and 18.3 mol dm-' respectively. The exchange parameters determined in CD3CN differ slightly from those determined in CD3N02 but in both cases the data are considered to typify a dissociative (D) solvent exchange mechanism. Dimethyl sulphoxide exchange on [Be(O=SMeZ),j2+ in CD3N02 diluent is characterised by an exchange rate = k2 [Be(O = SMez):'JIO = SMe2Jf,, for which k2(298.2 K) = 143 f 10 dm' m o l -'~-~, AH' = 51.1 rt 0.6 kJ mol-', and AS' = -32.3 * 2.2 JK-' mol-I, and which is considered to typify an associative (A) solvent exchange mechanism. Mechanistic comparisons are made with the data from other studies of solvent exchange on beryllium(I1). Fluoreszenz / Intersystem Crossing / Temperaturabhangigkeit / SubstituenteneinfluJThe energies of the excited states which are involved in the deactivation, the quantum yields of fluorescence and intersystem crossing, and the fluorescence decay times were determined fo...

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Photocatalytic cis→trans‐Isomerization of Thioindigoid Dyes

Klages

Kobs

Memming

1982

Ber Bunsenges Phys Chem

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The trans‐isomers of certain thioindigoid dyes in dilute solutions can be completely converted to the cis‐isomer by selective excitation of the trans‐isomer. At higher dye concentrations the conversion is limited. The corresponding photostationary state is determined by two processes in opposite directions: (i) by the usual trans→cis photoisomerization and (ii) by an inverse cis→trans isomerization initiated by excitation of the trans‐isomer. An analysis of this peculiar effect has shown that the trans‐triplet catalyses the cis→trans‐isomerization.

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Electron acceptor properties of excited trans-thioindigo

Cited by 9 publications

References 0 publications

Photoisomerization of N,N′-disubstituted indigos. A search for energy storage

Photoisomerization of N,N′-disubstituted indigos. A search for energy storage

A Proton NMR Study of the Dynamics of Ligand Exchange on Tetrakis(1,1,3,3‐Tetramethylurea)Beryllium(II) and its Dimethyl Sulphoxide Analogue

Photocatalytic cis→trans‐Isomerization of Thioindigoid Dyes

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