Bleaching Studies of Rose Bengal Onium Salts

Article abstract of DOI:10.1021/ja00212a038

The bleaching behavior of Rose Bengal onium salts containing one or two iodonium, sulfonium, and phosphonium ions in different solvents has been investigated.Fluorescence quenching of Rose Bengal sodium salts (Ia, IIa) by cationic onium salts (IIIa-d) and by the corresponding neutral species suggests a parallel exists between the rates of bleaching of the onium salts of Rose Bengal (Ia-c, IIa-d) and the fluorescence quenching of the sodium salts by the corresponding cationic salt, but not the neutral species.Quenching data combined with redox potentials measured by cyclic voltammetry, as well as preliminary product studies, indicate that the dye singlet is oxidized during the photobleaching process in cases where the gegen ion is strongly reducing.Nonreducing gegen ions cause photobleaching of the dye too, but at a much slower rate.In the latter case the triplet of the dye must be responsible for photobleaching since limited or no fluorescence quenching is observed.