In photosensitivity reactions

For a review of other complications that can take place in photosensitized reactions, see Engel, PS. Monroe, B.M. Adv. Photochem., 1971, 8, 245-313. 

With the possibility of so many side effects in photosensitized reactions, the question may well be asked, How can one make an intelligent choice of sensitizer Obviously the approach is more sophisticated than dump in some benzophenone. Although the answer will depend a great deal on the system under study, we shall attempt to provide a few general rules for the selection of a sensitizer. 

This energy-rich 02 has in water (H20) only a very short lifetime (k = 2.5 x 10s s 1 in D20 it lives much longer, k = 1.6 x 104 s 1). Singlet 02 shows often only a low reactivity, but with a series of compounds, including dGuo and its derivatives, it reacts quite rapidly (for a compilation of rate constants, see Wilkinson et al. 1995). Because of its prolonged lifetime in D20, the yields of 02(1Ag)-reac-tions are much higher in this solvent than in water. In photosensitized reactions considered to occur by a free-radical pathway, these 02(1Ag)-reactions may yield... 

Koizumi M, Kato S, Mataga N, Matsuura T, Usui Y (1978) in Photosensitized Reactions, Kagakudojiin Publ Co, Kyoto, Japan, Chaps 5, 11, 12... 

Colloidal Si02 particles in an aqueous suspension provide a solid-liquid interface. The silanol groups on the particle surface are ionized at a pH 6. Consequently, the surface of the particle is negatively charged and a diffuse electrical double layer is produced in the vicinity of the solid interface (17,18). Because of the negative charges on the particles they repel one another and their agglomeration is prevented. The particles can be used to exert electrostatic repulsive and attractive interactions with the components involved in photosensitized reactions. 

In photosensitized reactions, electron transfer occurs between the excited state of the sensitizer and amine resulting in the formation of the radical ion-pair. The sen-... 

Phenyl azide can yield benzotriazole on irradiation , but more generally products of self-insertion or of attack on the solvent are found to lead to azepines and related compounds " - . Photolysis of o-azidobiphenyls formed carbazoles by intramolecular cyclization similar to that found in thermolysis and an analogous intramolecular cyclization involving, e.g. a nitro group could occur (reaction 74) in direct photolysis but not apparently in photosensitized reactions when only azobiphenyl was formed in appreciable yield The... 

Spadoni G, Bandini E, Santarelli F Scattering effects in photosensitized reactions, Chem Eng... 

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