Photosensitizers singlet oxygen generation, Rose Bengal

Metal-Enhanced Singlet Oxygen Generation 10.3.1 1. Rose Bengal as a Photosensitizer... 

The photochemical generation of singlet oxygen has suffered from the insolubility of those anionic dyes which are commonly used as sensitizers (see Fig. 11.1). It has recently been found that the photosensitizing dyes eosin and rose bengal can be solu-... 

Perhaps more important, Foote has shown that chemically generated singlet oxygen gives the same product distribution from (+)-limonene as obtained by the rose bengal-photosensitized oxidation.467 Moreover, the (—)-tra 5,-carveol formed in both types of oxidation has the same large optical activity. 

Photosensitization using a dye is convenient and we employed this method for our work in environmental purification. Quantum efficiencies of generating singlet oxygen (,o2) using Rose Bengal, Methylene Blue, and Eosin, for examples, are known to be 0.80 0.50 and 0.42, respectively. Two mechanisms have been... 

Although simple acetylenes do not react with singlet oxygen that has been generated using methylene blue or Rose Bengal in MeOH, photosensitized oxygenation of aryl acetylenes is reported to occur in the presence of some cyanoaromatics and yields benzils (Scheme 5). Diphenylacetylene (39) also... 

Homogeneous photosensitization. Rose Bengal and Eosin-Y, anionic dyes used for generation of singlet oxygen, are not soluble in aprotic solvents. They can be solubilized in CS2 and CH2CI2 by complexation with 18-crown-6 or with Aliquat 336. 

The dye Rose-Bengal, in solution or as a suspension, is a very suitable sensitizer for generating singlet oxygen (Foote, 1%8 Kearns, 1971). There are several limitations to the dyes as photosensitizers (a) When the sensitizer is used in a solution, solvents which can be used for the reaction are limited, (b) The dye bleaches if longer reaction times are used, (c) The dye can sometimes react with the reactants or with the products, (d) Separation of the products from the dye in the reaction mixture is often difficult. 

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