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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"These data show that almost 90% of both aza-OIAs exchanged deuterium at position 4, as indicated by the 1 H NMR experiments. This unexpected H/D exchange observed for aza-OIAs encouraged us to test the isotopic exchange with the previously studied derivatives oxoisoaporphines, OIAs , and 2,3-dihydro- oxoisoaporphines, 2,3-dh-OIAs   . 3.3. "
[Show abstract][Hide abstract] ABSTRACT: During the 1H NMR study of the photoreduction of aza-oxoisoaporphines, aza-OIAs, (7H-benzo[e]perimidin-7-ones) by amines we found an unexpected H/D isotopic exchange in the aromatic positions 4 and 6 of these molecules. This surprising exchange motivated us to probe it with previously studied oxoisoaporphines, OIAs, (1-aza-benzo[de]anthracen-7-ones) and 2,3-dihydro-oxoisoaporphines, 2,3-dh-OIAs, (2,3-dihydro-7H-dibenzo[de,h] quinolin-7-ones). All of these compounds photoreduce efficiently in the presence of aliphatic tertiary amines through a stepwise mechanism of electron-proton-electron transfer. This photoreaction generates an AH - anion hydrogenated either at the N-atom, for 2,3-dh-OIAs, or at the O-atom for aza-OIA and OIAs. These long-lived metastable photoproducts revert thermally to the initial oxoisoaporphines nearly quantitatively. In the presence of D2O, regioselective exchange of the aromatic protons at positions 4 and 6 takes place to an extent greater than 90% under very mild conditions. This facile isotopic exchange reaction might be advantageously used to introduce deuterium, and likely tritium at these positions of aromatic oxoisoaporphines.
Full-text · Article · Aug 2011 · Journal of Photochemistry and Photobiology A Chemistry
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] ABSTRACT: Photoreduction by amines of oxoisoaporphine dyes occurs via a stepwise mechanism of electron-proton-electron transfer that leads to the metastable N-hydrogen oxoisoaporphine anion. During photoreduction that occurs from the triplet manifold of the oxoisoaporphine, a radical ion A(-)(*), a neutral-hydrogenated radical A-NH(*), and the metastable ion A-NH(-) of the oxoisoaporphine are formed. We present time-resolved spectroscopic data and quantum mechanical semiempirical PM3 and ZINDO/S results for the transient species formed during the flash photolysis of oxoisoaporphines in the presence of amines. These calculations reproduce adequately the experimental spectra of the triplet-triplet absorption near 450 nm, and that of neutral hydrogenated radical of the studied oxoisoaporphines centered at 390 nm. A transient absorption observed near 490 nm, for all of the studied systems, was explained by considering the formation of radical ion pair between the radical anion of the oxoisoaporphine, A(-)(*), and the radical cation of the amine, whose ZINDO/S calculated spectra generate the strongest transition near the experimentally observed absorption maximum at 490 nm, supporting the formation of a radical ion pair complex as the first step of the photoreduction.
Full-text · Article · Aug 2005 · The Journal of Physical Chemistry A