Photoinduced reactions, molecular oxygen

The interception of the radical anion by add or the formation of 28 should have the same effect. In fact, the back electron-transfer reaction from (TCA ) to (DPA ) is suppressed, or at least reduced, maximizing the cage escape efliriency of the radical cation and its further reaction with molecular oxygen. In these reactions benzil 26 is probably formed via the dioxete intermediate, also suggested by de Mayo and co-workers [100], whereas the mechanism leading to benzoic add is still uncertain. Other examples of photoinduced oxygenations, preceded by nucleophilic addition, have been also reported. 

Porphyrin derivatives have been extensively tested as photosensitizers for the PDT of cancer for two sets of reasons. First, their strong absorption of light in the phototherapeutic window and efficient photoinduced reactions with molecular oxygen offer a photochemical tool to induce localized cytotoxicity in targeted tissues. Second, porphyrin derivatives have an intrinsic affinity for tumors (4-6). Whereas the spectroscopy and photochemistry of porphyrin derivatives are very well understood, the same is not (yet) true for the mechanisms that contribute to their preferential localization and accumulation in tumors. This latter subject is outside the scope of this work, and it will only be briefly mentioned in the context of in vivo studies with porphyrin derivatives. 

Typically sunlight absorption can excite Fe(III) complexes to ligand-to-metal charge transfer (LMCT) excited states, which decay via photoinduced electron transfer (PET) to the Fe-center from the inner (ligand) or external electron donor. The photo-chemically generated Fe(ll) species is then reoxidized to the initial Fe(lll) compound or its derivative (e.g., aqua complex) closing the photocatalytic cycle. As result many environmental pollutants are oxidized by molecular oxygen in reactions driven... 

Photoinduced electron transfer studies have been performed in a more limited number of cases, due to the fact that the simultaneous presence of two reaction partners with appropriate characteristics is necessary. The study of suitably functionalized dendrimers can furnish information on the accessibility of the inner shell or core to external reagents (such as molecular oxygen or other small molecules) and on interchromophoric interactions within the dendritic structures. Electro-inactive dendrimers can also be important in regulating the electron transfer reactions between hosted partners in this sense dendrimers may also constitute a peculiar medium to investigate electron transfer reactions in restricted spaces. 

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

Kamata, M., Kato, Y., and Hasegawa, E., Photoinduced single electron transfer reactions of 1,3-dithianes and 1,3-dithiolanes sensitized by triphenylpyrylium salt in the presence of molecular oxygen. Tetrahedron Lett., 32, 4349,1991. 

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