- Photophysical and spectroscopic studies of indigo derivatives in their keto and leuco forms
-
A comprehensive spectroscopic and photophysical study of the keto and leuco forms of indigo and three other ring-substituted derivatives in solution was performed. The characterization involves absorption, fluorescence, and triplet-triplet absorption spectra, making it possible to obtain the quantum yields for fluorescence (φF), singlet-triplet intersystem crossing (φISC)> internal conversion (τIC), and lifetimes for fluorescence (τF) and triplet decay (τ T). For the case of the keto forms, pulse radiolysis experiments have revealed the existence of a triplet acceptor (from energy transfer from different donors) for the indigo, purple, and indirubin compounds. It is shown that with the keto form the major deactivation pathway involves internal conversion from the lowest singlet excited state to the ground state whereas with the leuco form there is competition between internal conversion, triplet formation, and fluorescence deactivation processes. Furthermore, leuco forms present much higher Stokes shifts compared with keto ones, suggesting an excited-state geometry different from the ground-state geometry, possibly involving rotational photoisomerization.
- Seixas De Melo,Moura,Melo
-
-
Read Online
- Characterization of the excited states of indigo derivatives in their reduced forms
-
A comprehensive characterization of the electronic spectral and photophysical properties of the leuco (reduced) form of several indigo derivatives, including indigo and Tyrian Purple, with di-, tetra-, and hexa-substitution, was obtained in solution. The characterization involves absorption, fluorescence, and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields of fluorescence, ΦF(0.46- 0.04), intersystem crossing, ΦT (0.013-0.034), internal conversion, ΦIC, and the corresponding lifetimes. The position and degree of substitution promote differences in the spectral and photophysical properties displayed by the investigated leuco derivatives. The ΦF values are about two orders of magnitude higher than those previously obtained for the corresponding keto forms. Also in contrast with the behavior found for the keto forms, the S1~~→T1 intersystem crossing is an efficient route for the excited-state deactivation channel. These findings strengthen the fact that, in contrast to keto indigo where the internal conversion dominates the deactivation of the excitedstate, with leuco indigo (and derivatives), the excited state deactivation involves competition between internal conversion, triplet state formation, and fluorescence. A time-resolved investigation of one of the compounds in glycerol showed the presence of a photoisomerization process.
- Rondao, Raquel,Sergio Seixas de Melo,Voss, Gundula
-
-
Read Online
- Direct electrochemical reduction of indigo
-
Increasing ecoefficiency of textile wet processes has become an important topic in our research group. Reducing agents required for the application of vat and sulfur dyes cannot be recycled, and they lead to problematic waste products. Therefore, modern aspects of economical and ecological requirements are not fulfilled. The application of direct electrochemical reduction of indigo as a novel route has been investigated by spectrophotometric and voltammetric experiments in laboratory cells. Experiments yield information about the reaction mechanism and the kinetics, and they show the possibility of this new route for production of water-soluble indigo, which offers tremendous environmental benefits.
- Roessler, Albert,Dossenbach, Otmar,Meyer, Ulrich,Marte, Walter,Rys, Paul
-
p. 879 - 882
(2007/10/03)
-
- Pyridazines with Heteroatom Substituents in Position 3 and 5. 2 . Regioselective Introduction of Mercapto Groups in Pyridazines
-
The nucleophilic substitution of halogen in 3,5-dichloro-6-phenylpyridazine 1, 5-chloro-2-methyl-6-phenylpyridazin-3(2H)-one 13 as well as in 3-chloro-2-methyl-6-phenylpyridazin-5(2H)-one 14 with methoxy, ethoxy, and the 2-methyl-2-propanethiolate anion is described.In the last type of compounds the t-butylthio groups can be eliminated regioselectively with Lewis acids, resulting in the formation of monomercapto and monothiopyridazines.
- Olesen, Preben H.,Kappe, Thomas
-
p. 1719 - 1723
(2007/10/02)
-
- Synthesis of N,N'-Diacylindigotins (N,N'-Diacyl-2,2'-bi-indolinylidene-3,3'-diones) via an Oxidative Oxygen-to-Nitrogen Acyl Shift of O,O'-Diacyl-leucoingigos(3,3'-Diacyloxy-2,2'-bi-indolyls)
-
O,O'-Diacyl-leucoindigos (3f-j), which were readily obtained by the reaction of leucoindigo disodium salt (4) with acyl chlorides, underwent rapid oxidation by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to fenerate the indigo chromophore with concomitant shift of the acyl groups intramolecularly from oxygen to nitrogen.A number of N,N'-diacylindigotins with functionalized acyl groups were prepared by this method and the direct N-acylation method .A large bathochromic shift of the visible absorption band in the cis form of N,N'-diacylindigotins with bulky acyl groups (2c), (2d), and (2j) was observed which suggested that the electronic structure of the indigo chromophore is perturbed by the steric constraint of the N-acyl groups.
- Setsune, Jun-ichiro,Wakemoto, Hirofumi,Matsueda, Taizo,Matsuura, Toshikazu,Tajima, Hideaki,et al.
-
p. 2305 - 2310
(2007/10/02)
-
- 5,6-Dihydro-1,2,4,6-thiatriazin-5-one-1,1-dioxides
-
5,6-Dihydro-1,2,4,6-thiatriazin-5-one-1,1-dioxides of the formula STR1 where R1 is hydrogen, a metal atom or an unsubstituted or substituted ammonium radical, R2 is a saturated or unsaturated straight-chain aliphatic radical of up to 10 carbon atoms, a cycloaliphatic radical or 3 to 7 carbon atoms, a branched saturated or unsaturated aliphatic radical of 3 to 10 carbon atoms, a halogen-, alkoxy- or alkylmercapto-substituted aliphatic radical of 2 to 10 carbon atoms tetrahydrofuryl substituted methyl, a cycloalkoxy-substituted aliphatic radical of 4 to 10 carbon atoms, unsubstituted or halogen-substituted benzyl or phenyl, halophenyl, or alkylphenyl of a total of up to 10 carbon atoms, R3 is hydrogen, a straight-chain aliphatic radical of up to 10 carbon atoms, a cycloaliphatic radical of 3 to 7 carbon atoms, a branched aliphatic radical of 3 to 10 carbon atoms, haloalkyl, or alkoxyalkyl of 2 to 10 carbon atoms and X is oxygen and may also be sulfur if R2 is unsubstituted or halogen-substituted benzyl, processes for their preparation, and herbicides containing the above compounds.
- -
-
-
