Photochemistry, molecular Photosensitizer

Inoue, Y. (2004) Enantiodifferentiating photosensitized reactions, in Chiral Photochemistry (Molecular and Supramolecular Photochemistry), Vol. 11... 

Photochemistry. Molecular hydrogen containing traces of mercury vapour (photosensitizer) is irradiated by UV radiation (A = 253.7nm). The gas can then bring about... 

Photosensitization The process by which a photochemical or photophysical alteration occurs in one molecular entity as a result of initial absorption of radiation by another molecular entity called a photosensitizer. In mechanistic photochemistry the term is limited to cases in which the photosensitizer is not consumed in the reaction. 

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. 

The polyacrylophenones represent another important category of photosensitive polymers. Substitution on the phenyl ring can alter both the efficiency and mechanistic pathway to reaction products (38). Early work (39) showed that the photochemistry could be related to that of small-molecule analogs. Work at the Slovak Academy of Sciences (40) has extended to a very large number of substituted derivatives. In common with other ketone systems, the quantum yields for chain scision are reduced significantly in the solid phase. Some of this is due to the restrictions on molecular mobility, which reduce the quantum yields of type-II photoprocesses. Another important factor is the extensive triplet migration, which, in the solid phase, leads to quenching by reaction products (41), such as the olefin produced by the type-II photoprocess. 

The triplet photochemistry of propylene has also been studied by several laboratories and in different conditions (40). Cis-trans isomerization is the main process and is observed in the presence of various sensitizers. As far as fragmentation is concerned, the C-C and C-H bond ruptures are observed in a 0.125/1.0 ratio (40a). In the case of the Hg( Pi) photosensitization of trans-propylene-l,3,3,3-rf4, no isomerization to propylene-2,3,3,3- /4 was observed. This is in marked contrast to the observation of the internal 1,2-hydrogen atom transfer observed in ethylene (40c). There is also formation of tiny amounts of cyclopropane and molecular methane and hydrogen (40). 

Turro NJ (1991) Modem molecular photochemistry. University Science, Sausabto Xiao L, Gu L, Howell SB, Seilor MJ (2011) Porous sibcon nanoparticles photosensitizers for singlet oxygen and their phototoxicity against cancer cells. ACS Nano 5(5) 3651-3659... 

These NSAIDs are photolabUe and are known to exhibit phototoxicity, causing a number of side effects such as dizziness, drowsiness, nausea, and gastrointestinal tract irritation. Many of them can also induce skin photosensitivity in some patients. In addition, ketoprofen, one of the commonly prescribed NSAIDs, produces photohemolytic activity toward red blood cells and is also capable of causing photocleavage of DNA. - The photosensitization of NSAIDs can be traced to their photochemistry and, upon excitation, decarboxylation is the major reaction pathway. " The aryl methyl radical can then react with molecular oxygen to yield a peroxide radical. It can also undergo coupling and other related radical reactions. 

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