Photosensitization, definition

Foote, C. S. (1991). Definition of Type I and Type II Photosensitized Oxidation. 

Foley S, Crowley C, Smaihi M, Bonfils C, Erlanger BF, Seta P, Larroque C (2002) Cellular localisation of a water-soluble fullerene derivative. Biochem Biophys Res Commun 294 116-119. Foote CS (1991) Definition of Type-I and Type-II photosensitized oxidation. Photochem Photobiol 54 659-659. 

Ru(CN)jNO reactions with OH , SH and SOj" resemble those of the nitroprusside ion, with attack at the coordinated nitrosyl to give analogous transients and similar second-order rate constants. Ruthenium(II) complexes of the general type Ru(N2), Nj = biden-tate hgands, are important reactants. The relative inertness of Ru(NH3) + and Ru(diimine)f+ towards substitution makes these complexes definite, although weak, outer-sphere reductants (Tables 5.4, 5.5, 5.6 and 5.1). Ruthenium(ll) complexes of the general type Ru(diimine)f +, and particularly the complex Ru(bpy)j+, have unique excited state properties. They can be used as photosensitizers in the photochemical conversion of solar energy. Scheme 8.1 ... 

Photoconductivity is one of the most informative phenomena in semiconductor physics. The light beam enables us to exite definite energetic levels strongly and obtain information about photogeneration, recombination and transport processes of the charge carriers. The history of photoconductivity shows the every essential step in research and application has been linked with the appearance of new photosensitive materials with specific physico-chemical properties. 

Definition of porphyrias, their modes of genetic inheritance, and their treatment Porphyrias are caused by inherited (or occasionally acquired) defects in heme synthesis, resulting in the accumulation and increased excretion of porphyrins or porphyrin precursors. Porphyrias are classified as erythropoietic or hepatic, depending where the enzyme deficiency occurs. With the exception of congenital erythropoietic porphyria, which is a genetically recessive disease, all the porphyrias are inherited as autosomal dominant disorders. All porphyrias result in a decreased synthesis of heme and, therefore, ALA synthase is dere-pressed. The severity of symptoms of the porphyrias can be diminished by intravenous injections of hemin. Because some porphyrias result in photosensitivity, avoidance of sunlight is helpful. 

Those photosensitive systems mentioned above consist of at least one vinyl compound which has an electron donating or accepting property. When both acceptor and donor are non-polymerizable, the system is not photosensitive. Photopolymerization of styrene is not sensitized by the ECZ-CH3CN pair. The definition of donor and acceptor is a matter of relativity. Styrene is by no means neutral, but there should be no objection to considering it as a weaker donor than VCZ or ECZ and a weaker acceptor than AN or CH8CN. Photoirradiation of AN, VCZ or styrene alone in a neutral solvent, such as benzene, or in bulk does not bring about any appreciable rate of polymerization. 

Schenck and Steinmetz [26] have found that the addition of maleic anhydride to benzene can be photosensitized by benzophenone. The photosensitized reaction also works with toluene, o-xylene, and chlorobenzene. Hardham and Hammond [27,28] have also studied the photosensitized addition and they obtained definitive evidence that this reaction proceeds via the triplet state. They also proposed an ortho adduct as intermediate but were unable to isolate it. Bryce-Smith and Vickery [29] found that phenanthrene reacts with maleic anhydride at the 9,10-positions to give an adduct that does not further react with a molecule of maleic anhydride. This reaction can also be sensitized by benzophenone. 

Foote CS (1991) Definition of type-I and type-II photosensitized oxidation. Photochem Photobiol 54 659-659... 

Substrates containing an electron-rich double bond, such as enol ethers and enol acetates, are easily oxidized by means of PET to electron-deficient aromatic compounds, such as dicyanoanthracene (DCA) or dicyanonaphthalene (DCN), which act as photosensitizers. Cyclization reactions of the initially formed silyloxy radical cation in cyclic silyl enol ethers tethered to an olefinic or an electron-rich aromatic ring, can produce bicyclic and tricyclic ketones with definite stereochemistry (Scheme 9.14) [20, 21]. 

Figure . Proposed reaction scheme for BTD-photosensitized reduction of AQDS by MES in CTAB micelles (adapted from [73]). BTD is either BTDB or BTDE (see text for definitions).

A major advantage of organic polymers is the possibility of photo-definition. The use of a photosensitive dielectric greatly simplifies processing by eliminating the application, processing, and removal of a separate photoresist. With the decrease in processing steps comes an increase in the yield of circuits. 

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