Xanthene dyes Rose Bengal

Dye-Based Systems Many compounds can be used [lh,i]. Classical examples are found in the numerous available dyes and colored molecules [li] such as xanthenic dyes (Rose Bengal, eosin [194,195], etc.), thiazines (methylene blue, etc.), acridines, /V-methylacridone, phenosaffanines, thiopyronines, riboflavines [196,197], pheno-xazines [198], pyrromethenes [199], polymethines, fluorones, squarylium [200], julolidine dyes, and so on. (see, for example, Rose Bengal, acriflavine, and acridine orange in (10.57)). 

Reduction of (R)-(+)-citronellal by lithiumaluminumhydride yields (R)-(+)-citro-nellol which undergoes a photo ene reaction to the hydroperoxide in the presenee of the xanthene dye rose Bengal as a photosensitizer of singlet-oxygen. Sodium sulfite reduces hydroperoxide to the diol which is, when catalyzed by acids, dehydrated to the ir s-isomer of rose oxide... 

Quite a number of the classes of photoreducible dyes have been identified. These include the xanthenes (fluorescein, rose bengal), the thiazines (methylene blue, thionine), the acridinium dyes (acriflavin), and some natural products, such as riboflavin " ... 

Dyes, xanthene used for eosin, fluorescein-type phthaleins, rhodamines, and rose Bengal. 

With rose bengal and erythrosin as xanthene dye sensitizers, the... 

Electron transfer to the xanthenes, particularly reduction with amines, has been used for a number of years to initiate acrylate polymerization. A typical system is that reported to form volume holograms—lithium or zinc acrylate, triethanolamine and Eosin, Erythrosin, or Rose Bengal [290], Similar mixtures are used to form printing plates photoreducible dye, phenylac-ridine, and acrylate monomer [292], A recent patent application discloses aryl iodonium salts, Rose Bengal, and oxidizable triazines such as 2-methyl-4,6-bis(trichloromethyl)-s-triazine to polymerize acrylates [292],... 

This chapter has concentrated on the photochemistry, photophysics, and numerous applications of the hydroxyxanthenes, among the most versatile of the synthetic dyes. The literature concerning Rose Bengal seems to have grown most rapidly in recent years, in large measure because of its numerous applications. As we have studied these systems over many years, we find that their chemistry is rational, though complicated, and their spectroscopy, rich with information, is rewarding. We have tried to cover the subject broadly, but there is no possibility that we could do so exhaustively. We hope that readers will bear that in mind, and share additional information about the xanthenes and related systems with us as it comes to their attention. 

The formation of donor-acceptor complexes between bipyridinium salts (electron acceptors) and xanthene dyes (electron donors) (e.g., eosin. Rose Bengal) has been studied extensively. Crystal structures of these complexes have been identified, and the structural features of the donor-acceptor complexes in solutions have been characterized using NMR spectroscopy. The xanthene dye/bipyridinium donor-acceptor complexes are stabilized by... 

The acid xanthene dyes comprise Eosin (tetrabromofluorescein, formula 4.34) [79,80], Erythrosin (tetraiodofluorescein) and Rose Bengal B (formula 4.35) [79]. All these reagents are available as sodium salts. 

Use has been made of ion-pairs formed by the cationic complex of zinc with 1,10-phenanthroline or 2,2 -dipyridyl and acid dyes, such as eosin, Erythrosin, Rose Bengal, dibromofluorescein (xanthene dyes) [72-74], Bromophenol Blue, Bromophenol Red (triphenylmethane dyes) [75,76]. In some of these methods, molar absorptivities are -10. Chloroform is the usual extraction solvent. 

Rose Bengal xanthene dye photosensitizer, 277 Ruthenium, dihydrotetrakis(triphenylphosphine)- double bond shift in alkenes, 270 Ruthenium(2 +), chiral binap complexes asym. hydrogenation with, 102-103, 325-326 Ruthenium(8 +) oxide oxidation with of alcohols to ketones (catalytic), 267 of alkynes to 1,2-diones (catalytic), 117, 132 of ethers to esters, 118, 134-135... 

The dye-sensitized photo-oxidation of phenols has been examined using CIDNP techniques.148 It is concluded from the observed polarizations of nuclear spin that sensitization by xanthene dyes (such as Rose Bengal) is the result of reversible hydrogen abstraction by the triplet dye molecule from the phenolic hydroxyl group. Any resulting photochemical reactions (e.g. with oxygen) arise from irreversible reactions of the phenoxy-radicals produced, rather than from direct reactions of the phenols with 102. Dye-sensitized photo-oxidation of p-hydroxyphenylpyruvic acid (94) in solution at pH 7 (conditions under which... 

H-aggregation of methyl orange has been postulated to account for the hypsochromic shift of the dye in a water-in-oil microemulsion, with the dye molecules in a parallel orientation at the interface beween the water and the oil phase. The observation of salt-induced strongly red-shifted J-bands in aqueous solutions of Rose Bengal, an anionic xanthene dye, in the presence of zwitterionic surfactants was... 

---