Photoreduction of oxoisoaporphines. Another example of a formal hydride-transfer mechanism.
ABSTRACT Photoreduction of 5,6-dimethoxy-, 5-methoxy- and 2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one (A) by tertiary amines in oxygen-free solutions generates long-lived semi-reduced metastable photoproducts, A-NH(-), via a stepwise electron-proton-electron transfer mechanism with a limit quantum yield of about 0.1 at high TEA concentrations. These metastable photoproducts revert thermally to the initial oxoisoaporphine nearly quantitatively in the presence or absence of oxygen. We present spectrophotometric, NMR and UV-vis data for the metastable photoproducts. The spectrophotometric results and PM3 and ZINDO/S calculations support the proposed mechanism for the photoreduction of the oxoisoaporphines.
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ABSTRACT: The new oxoisoaporphines 7H-dibenzo[de,h]quinolin-7-one, 5-methoxy-7H-dibenzo[de,h]quinolin-7-one, 5-methoxy-6-hydroxy-7H-dibenzo[de,h]quinolin-7-one, 5-hydroxy-7H-dibenzo[de,h]quinolin-7-one and 5-methoxy-6H-dibenzo[de,h]quinolin-6-one were prepared either by oxidation of their 2,3-dihydro derivatives or by heating (2'-(3,4-dihydro-6,7-dimethoxyisoquinolin-1'-yl)phenyl)methylbenzoate with an acetic acid/sulfuric acid mixture at 100 degrees C. The structures were confirmed and 1H and 13C NMR spectra were completely assigned using two-dimensional NMR techniques.Magnetic Resonance in Chemistry 01/2006; 43(12):1080-3. · 1.53 Impact Factor
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ABSTRACT: SeaWiFS and MERIS capabilities for the estimation of optically active components in ocean waters are analysed by means of a semi-theoretical model of ocean colour which also takes account of the chlorophyll fluorescence signal at about 685 nm. The reflectance curves simulated with the model over various types of water have been integrated over the bands of the two sensors, and a regressive analysis has been used to find the algorithms for the retrieval of the three main classes of optically active components, and the corresponding correlation coefficients. The results show that the availability of SeaWiFS data will give unprecedented capabilities for the retrieval of optically active parameters from satellite imagery, especially over case 1 waters. MERIS will have the same potential in those waters; moreover, the presence of two additional channels in the red region makes this instrument very interesting also for the parameter retrieval over case 2 watersGeoscience and Remote Sensing Symposium, 1996. IGARSS '96. 'Remote Sensing for a Sustainable Future.', International; 07/1996
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ABSTRACT: Photoinduced electron transfer between N-phenylglycine and electronically excited triplets of 7-substituted-3-methyl-quinoxalin-2-ones in acetonitrile generate the respective ion radical pair, where by decarboxylation the phenyl-amino-alkyl radical, PhNHCH2 •, is generated. This radical reacts with the 3-methyl-quinoxalin-2-ones ground states, leading to the products 2. Other, unexpected, 7-substituted-1,2,3,3a-tetrahydro-3a-methyl-2-phenylimidazo[1,5-a]quinoxalin-4(5H)-ones, annulation products, 3a-f, were generated; likely by the addition of two PhNHCH2 • radicals, to positions 3 and 4 of the quinoxalin-2-ones. A reaction mechanism includes a photoinduced one electron transfer initiation step, propagation steps involving radical intermediates and NPG with radical chain termination steps, leads to the respective products 2a-f and 3a-f and NPG by-products. The proposed mechanism account for the strong dependency found for the initial photoconsumption quantum yields on the electron withdrawing power of the substituent. Therefore photolysis of common reactants widely used such as NPG and substituted quinoxalin-2-ones may provide a simple synthetic way to the unusual, unreported tetrahydro-imidazoquinoxalinones 3a-f. This article is protected by copyright. All rights reserved.Photochemistry and Photobiology 08/2013; · 2.29 Impact Factor