Sensitizer tetraphenylporphine

Weak electron acceptors with low triplet energies18 should be used as sensitizers. Tetraphenylporphin (34.0 keal/mol). metalloporphyrins (e.g.. zinc tetraphenylporphin), and hematoporphyrin (37.2 keal/mol) are suitable. Rose bengal (39.2-42.2 keal/mol) can be cm-... 

The Methylene Blue sensitized photoaddition of singlet oxygen to ethyl l//-azepine-l-car-boxylate was reported originally to yield only a C2-C5 adduct 269 however, a reinvestigation with the methyl ester, and using tetraphenylporphine as a sensitizer, revealed that in addition to adduct 46 the [6 + 2] cycloadduct 47 is also produced.270... 

Irradiation of the bis-alkene 210 brings about the formation of the bishomocubane 211 in good yield98. The triene 212 is of interest and has been shown to be photochemically reactive, yielding the adduct 213 on irradiation. Several approaches to 212 have been reported over the years. One such approach follows the path of photocyclization of 214 to yield 215 that can be converted to the desired product 21299. A variety of sensitizers can be used for the excitation of alkenes to bring about the (2 + 2)-cycloaddition. Commonly, acetone has been used but, in at least one case, the formation of the cage compound 216 from the diene 217, tetraphenylporphine has been found to be of use100. 

MI1 55CRV9, p.99). It was later prepared by coupling of 4-isopropyl-p-tropoquinone with 5-hydroxyhinokitiol or by a biomimetic photooxidation of hinokitiol (161) sensitized by tetraphenylporphin (83CL1371). These reactions exemplify the phenol oxidation in troponoid chemistry. 

Beside xanthene dyes, methylene blue,127 porphyrins and por-phins,128-130 zinc-tetraphenylporphin,128 a-hydroxyanthraquinones in alkaline alcoholic or pyridine solutions,112,131 vitamin A, /9-carotene, hypericin, rubrene, 3,4-benzpyrene, 20-methylcholanthrene, chlorophyll, and many other compounds have been found to be sensitizers of photooxygenation reactions.70,132,133 Some groups of dyes, however, such as porphyrins and porphins containing transition metals (e.g., Co), azo dyes, cyanine dyes, and triphenylmethane dyes either did not show any or only very poor sensitizer capabilities in the photooxygenation of a-terpinene.128,134... 

A number of acyl silanes have been isolated from the photosensitized oxygenation of silyl diazo compounds using meso-tetraphenylporphine (TPP) as the sensitizer (Scheme 15)15. This synthesis is most useful for aromatic acyl silanes and the yellow u-carboxyacyl silanes, but it is not of general applicability, isolation difficulties commonly being encountered in the synthesis of aliphatic and other acyl silanes, resulting in poor overall yields. 

Suitable light sources for exciting the sensitizer include halogen or mercury lamps equipped with a 400 nm cut-off filter to transmit visible light. The sensitizers methylene blue (MB), meso-tetraphenylporphine (TPP), sulfonated aluminum phtha-locyanine, and Rose Bengal (RB) are widely used in homogeneous solutions. The main appeal of heterogeneous sensitizers is that they are easy to separate from... 

On the contrary, a different stereochemical course was observed in the dye-singlet, DCA-photosensitized and electrode-catalyzed oxygenations of two stereoisomeric derivatives such as syn- and anfi-di-Jert-butylbis (bicyclo [3.3.1] non-9-ylidenes) 32. In fact, the tetraphenylporphine (TPP) and/or DCA-sensitized... 

This explanation was shown to be incorrect by investigation 95) of reactions of a number of a-diketones (benzil, biacetyl, 1-phenyl-1,2-propanedione) in the presence of olefins in oxygen saturated solutions. Slow consumption of diketone was observed with relatively rapid consumption of olefin and concomitant formation of epoxides, often in high yield. Many of the olefins which underwent this reaction do not form epoxides at all with singlet oxygen. For example, tetraphenylporphin-sensitized photooxygenation of tetramethylethylene afforded hydroperoxide 111 quantitatively while a biacetyl-sensitized reaction yielded the epoxide 112. Further, it was shown that the... 

The extinction coefficient of triplet benzophenone has been remeasured as 7220 320 dm moF cm at 530 nm and this has been used to measure the triplet yield for zinc tetraphenylporphine. The sensitization of naphthalene by benzophenone has been examined in different hydrocarbon or ethanol-ether glasses.Internal heavy-atom effects on the T, states of monochloro-... 

Zinc tetraphenylporphine has been found to sensitize the photoredox reaction between N-phenylglycine and p-benzoquinone in polar solvents. In MeCN and at wavelengths above 500 nm, the ketone is reduced to hydro-quinone, and following decarboxylation of the glycine to PhN=CH2 and hydrolysis, aniline is formed. In ethanol solution, photosensitized reduction... 

Numerous papers have appeared discussing the oxidation of hydrocarbons. For example, the effects of pressure on product yields in the nitrogen oxide (NO ) photo-oxidations of aromatic hydrocarbons such as toluene and o-xylene have been described and a study has been reported of the mechanism of the photo-oxidation of /3,/3-dimethylstyrene. Photo-oxidation of cis-a,a -dimethylstilbene using [Ru(bipy)3] or tetraphenylporphine as sensitizer leads to the dioxetane (19), whereas with Rose Bengal or Methylene Blue the... 

Tetraphenylporphine-sensitized photooxygenation of E,E)- or ( ,Z)-l-ar-ylpenta-1,3-dienes gives most of the cw-endoperoxides, m-3-aryl-6-methy 1-1,2-dioxacyclohex-4-enes, in a process which occurs by exclusive addition of 02( Ag) to the ( , )-dienes formed by photoisomerisation of the ( , Z)-dienes,... 

The photosensitized singlet oxygenation of 1,4-dioxins in methylene chloride at — 78°C using tetraphenylporphin as sensitizer affords the corresponding bisdioxetanes (74). In all photooxygenations, variable amounts of the corresponding a-diketones (75) and enediol diesters (76) were formed. Thermal decomposition of the bisdioxetanes (74) yielded the corresponding anhydrides... 

Dye-sensitized photooxygenation of a-pyrones and a-pyrans offers the simplest access to 1,2,4-trioxanes. Examples are the conversions of (36) to (37), and (40) to (41). The photooxygenation of a-pyran (164) in methylene chloride at 0°C using tetraphenylporphin as sensitizer and a 400 W sodium lamp gives (165) (Equation (20)) <78AG(E)2ii>. 

Competitive photooxygenatloa with srasltlzer 1. methylene blue 2, rtd>rene 3. zinc tetraphenylporphine 4. rose bengal. B Direct method employing laser pulse excitation of sensitizer 1. methylene blue ... 

Photooxygenation of Ge—Ge bonds. Photooxygenation of the digermirane 1 or the azadigermiridine 2 with tetraphenylporphine (TPP) as sensitizer affords cyclic peroxides (3 and 4, respectively). 

Chart 8.7 Sensitizers employed in the photochemotherapy of cancer cells. TPP meso-tetraphenylporphine, TMPyP meso-tetra 4-/V-methylpyridyl)porphine, MB methylene blue,... 

Cycloadditions.—Continuing interest has been shown in the photo-oxygenation of adamantylideneadamantane and in the reverse, thermally initiated, chemiluminescent fragmentation. Photo-oxygenation of the olefin affords the dioxetan (313) and the epoxide (312). With /ncso-tetraphenylporphin as sensitizer, (313) is the major product in all the solvents studied, whereas photo-oxygenation of the olefin in acetone and using a variety of dye sensitizers led to marked changes in the (312) (313) ratio. ... 

Optochemical Ethylcellulose, poly(hexylmethacrylate) Sensitivity smaller but faster recovery time compared to that of tetra-hydroxy-substituted tetraphenylporphin... 

A soln. of 2-(2-methyl-l-propenyl)thiophene and a little tetraphenylporphine as sensitizer in CCI4 irradiated ca. 0.5 hr. under Og with low-pressure Na-vapor lamps until an equimolar amount of oxygen has been absorbed product. Y 75%. F. e. s. M. Matsumoto, S. Dobashi, and K. Kondo, Tetrah. Let. 1975, 4471 Am. Soc. 99, 2393 (1977). 

The ratio of epoxide to dioxetane increased 28-fold on going from methylene chloride to benzene with tetraphenylporphin as sensitizer, such solvents as pinacolone, dioxan, and acetone occupying intermediate positions. Systematic investigation showed that epoxide more often than not accompanies the dioxetane from sensitized oxygenation of norbornene (22) and of biadamantylidene (H. J. Shapiro, quoted in (23) (26)). For each solvent-sensitizer combination, the ratio of epoxide to dioxetane increased in the order biadamantylidene < norbornene binor-bornylidene. This is also the decreasing order of reactivity of these olefins toward singlet oxygen. 

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