Photochemical Sensitization

Free radicals, generated in a sensitized photochemical process, also react at position 4 of perfluoropyridine [104, 105] (equation 53). 

Pt/Ru bimetallic nanoparticles. In the case of dye-sensitized photochemical water splitters, to which much attention has been received recently, noble metal nanoparticles are often used for the active centers to produce hydrogen gas from water. Bimetallic nanoparticles will be easily replaced by these metal nanoparticles for the sake of saving resources. 

Not all sensitized photochemical reactions occur by electronic energy transfer. Schenck<77,78) has proposed that many sensitized photoreactions involve a sensitizer-substrate complex. The nature of this interaction could vary from case to case. At one extreme this interaction could involve a-bond formation and at the other extreme involve loose charge transfer or exciton interaction (exciplex formation). The Schenck mechanism for a photosensitized reaction is illustrated by the following hypothetical reaction ... 

Johnston, H. S., and K. Dev Jain. Sulfur dioxide sensitized photochemical oxidation of hydrocarbons. Science 131 1523-1524, 1960. 

There are photocalorimetric enthalpy data for two other ozonides, both coming from sensitized photochemical dioxygenation reactions in non-polar solvents . This study reports the enthalpies of the reactions of 2,5-dimethylfuran and 1,3-diphenylisobenzofuran to their corresponding endoperoxides to be exothermic by —45 20 and —92 25 kJmoU (the latter value is an average of the values given for different solvents). From... 

Another approach to wards photocatalysis is to use dy as a sensitizer instead of a semiconductor as in photosynthesis. It is not the aim of this book to cover all the aspects of the sensitized photochemical conversion system, but typical sensitized systems for photocatalytic reactions of water are described in Chapter 18 The concept of a photochemical conversion system using a sensitizer and water oxidation/reduction catalysts is mentioned in Chapter 19, accompanied by a discussion on the sensitization of semiconductors. 

The sensitized photochemically-induced [2 + 2] cycloadditions of silyl enol ethers with acrylonitrile or methyl acrylate have been found, because of the regiospecificity of the... 

Bradshaw [74] reported in 1966 that maleimide undergoes sensitized photochemical addition to benzene, producing the imide analog of the corresponding maleic anhydride photoadduct. The author observed that the reaction probably proceeds by the addition of electronically excited maleimide to benzene. The photoaddition proved successful also with toluene, /-butylbenzene, and ethylbenzene. Simultaneously, Bryce-Smith and Hems [75] reported that 2 1 photoadducts are formed from maleimide, iV-n-butyl-,. V-benzyl-, iV-o-tolyl-, and iV-2,6-xylylmaleimide with benzene.. V-Phenyl, N-p-tolyl-, and A-p-methoxyphenylmaleimide did not form photoadducts. Trifluoroacetic acid was found to be virtually without effect on the photoaddition of N-n - bulyI maleimide No phenyl-A- -butylsuccinimide was detected [36], It was concluded that a dipolar intermediate is not involved. When N-n-bulylmalcimide and benzene were irradiated in the presence of tetra-cyanoethylene, a 1 1 1 adduct was formed [37],... 

Molecular mechanisms in nucleic acid photochemistry I. Sensitized photochemical splitting of thymine dimer. J. Amer. chem. Soc. 88, 813 (1966). 

Lunak S, Sedlak P, Lederer P. Methylene-blue-sensitized photochemical hy-droxylation of 2-hydroxybenzoic acid by hydrogen peroxide photocatalytic effect of ferric chloride. J Photochem 1987 39 239-250. 

Suginome, H. and Kobayashi, K. (1988) A reinvestigation of a sensitized photochemical cycloaddition of coumarin with cyclopentene. Bulletin of the Chemical Society of Japan, 61, 3782-3784. 

Molecular orbital computational analysis by PM3 CI UHF semiempirical methods have been used to support the contention that preferable HSOMO-LUMO interactions produce a favored biradical and explain the site selectivity in the sensitized photochemical [2 + 2] cycloadduct formation of 2-pyrones with electron-deficient ethylenes <92BCJ354>. The lowest ionization energies, dipole moment, and dominant electronic configurations of a 5-methylidenated version of 7-nitroso-oxazolo[4,5- ]cyclopenta[e]pyrimidine of unknown origin were calculated by the ADC(3) ab initio method <92CPHii>. An extensive semiempirical and ab initio investigation into the mechanism of oxidation of methanol by PQQ is cited in Section 7.22.12.4. 

The methylene blue-sensitized photochemical addition of singlet 02 to 5-alkoxyoxazoles in the presence of DABCO gives high yields of 1,2,4-dioxazolines (131) via a 1,2-addition of oxygen (Scheme 50). The DABCO is believed to inhibit the more commonly observed 1,4-cycloaddition pathway (77S572). 

The full paper on the photo-isomerization of cis -verbanone has been published (Vol. 4, p. 61) trans -verbanone gives the same products but in opposite proportions.308 Direct, and sensitized, photochemical rearrangement of 4-methylverbene (229) gives 3-methylenelimonene, from the corresponding triplet biradical, in... 

Kelly GE, Meikle WD, Moore DE. Promotion of UV-induced skin carcinogenesis by azathioprine role of photochemical sensitization. Photochem Photobiol 1989 49 59-65. Moore DE, MaUesch JL. Photochemical interaction between triamterene and hydro-chlorthiazide. Int J Pharm 1991 76 187-190. 

Hydrogen atoms generated from H in an electrical discharge, by thermolysis of Hj or in a Hg-sensitized photochemical process react with Sb targets to form SbHj in low yields ... 

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