Photosensitizers eosin

A characteristic property of those systems is the influence of photosensitizers (eosin, methylene blue). Schenk suggests (1948) that the... 

The scope extends to certain aromatic compounds such as phenanthrene. Besides those dienes and aromatic rings that can be photooxidized directly, there is a larger group that give the reaction in the presence of a photosensitizer such as eosin (see... 

Photolysis of nicotine (173) in the presence of oxygen and methylene blue with light wavelengths greater than 300 nm gave the pyrrolidone (174, 30%), nicotyrine (175, 23%) and TV-oxide (176, 7%). Under nitrogen, with eosin as photosensitizer, only nicotyrine (14%) was identified in the photodegraded mixture [112]. 

The covalent bonding of photosensitizer moieties such as benzophenone, rose bengal, and eosin to polystyrene yields polymeric photosensitizers that can be used to bring about excitation and subsequent chemical reaction in low-molecular-weight substrates [Neckers, 1986 Nishikubo et al., 1989]. 

It has recently been shown by Spikes150 that uracil and a number of substituted uracils are subject to dye-sensitized photooxidation under certain conditions. Methylene blue and Eosin Y were active photosensitizers in the pH range 8-11.5, but were inactive below pH 8. FMN was very active over the pH range of 2.4-11.5. Photooxidation was measured with a rotating platinum oxygen electrode. 

Photosensitized electron injection in colloidal TiOz has been reported by Moser and Gratzel as part of a scheme to photoreduce water [155], Moser et al. [156] and Rosetti and Brus [157] saw the formation of semioxidized Eosin by monitoring its absorption in the visible and by Raman spectroscopy. No oxidation of the triplet of Eosin adsorbed in Ti02 is observed, the lifetime... 

Photosensitized photooxidation of pyrrole (412) by irradiation in the presence of eosin gives rise to the photoproduct (413), presumably via the intermediate peroxide (414).440 Transannular peroxides are... 

A closely related organized microheterogeneous system has been composed of a Si02 colloid on which a Pd catalyst is immobilized, and the photosystem includes eosin, Eo2 (2), as photosensitizer, iV,A -dibenzyl-4,4 -(3,3 -dimethyl)bipyridinium, BMV2+ (15), as electron relay and TEOA as electron donor [137]. In a... 

In true photosensitized autoxidation, the addition of a sensitizer, such as chlorophyll, eosin, or rose bengal, is essential. This method was pioneered by Windaus and Brunken178 in the steroid series (ergosterol peroxide) and by Schenck and Ziegler179 in the terpene series (ascari-dole). Schenck et al.10 180,181 generalized the applicability of photosensitized autoxidation. 

Schenck and Ziegler170 obtained the naturally occurring endoper-oxide ascaridole (166) by irradiation of an alcoholic solution of a-terpinene in the presence of eosin. Endoperoxides similar to 166 are formed in the photosensitized autoxidation of cyclopentadiene,182 cyclohexa-1,3-diene,179,182 cyclohepta-1-3-diene,183 and their phenyl-... 

In this case, the activated compound (C) cannot be produced by direct irradiation with light of frequency v. Instead, the activated photosensitizer (Z) transfers energy to tiie monomer or initiator at an appropriate frequency that can be absorbed by C. Typical photosensitizers used in photochemically-initiated polymerizations are benzophenone, fluorescein, and eosin. 

Irradiation of aqueous solutions of (5)-tryptophan at pH 6-9 containing a photosensitizer (e.g., eosin) caused destruction of the amino acid and formation of N -formylkynurenine as the major product. Similar irradiation in dilute ammonia at pH 8-9 gave an optically active compound in 13% yield, which was shown to be 4-(2 -amino-2 -carboxyethyl)quinazoline (12). 

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... 

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. 

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