SINGLET OXYGEN PHOTOGENERATION BY IONIZED AND UN-IONIZED DERIVATIVES OF ROSE-BENGAL AND EOSIN Y IN DILUTED SOLUTIONS

Quantum yields of singlet oxygen photogeneration (relative to commercial Rose Bengal) were determined for the pure dye, Eosin Y, their corresponding methyl, benzyl, and p-isopropylbenzyl esters, and the product of Rose Bengal decarboxylation, all in solution in basic methanol (in order to assure total ionization). The similar values found for each series of salts indicate a low influence, if any, of the different C-2′ groups on their behaviour as sensitizers. As expected, the monodehalogenated parent dyes showed in the same medium somewhat lower yields. Slightly lower values were also found for the un-ionized forms of the methyl esters and for the non-ionizable methyl ether of Rose Bengal methyl ester in acidic dioxane as medium. In order to avoid the formation of dye aggregates and the quenching of the triplets of the sensitizer by the acceptor, all the yields were determined using solutions of 10-5 M sensitizer and 10-4 M or 10-5 M acceptor. The methodology, including the spectrophotometric procedure used to determine relative β values, is also reported. © 1990.