Photophysical investigation of Rose Bengal in aqueous sodium taurocholate solutions

The photophysics of rose bengal has been studied in aqueous sodium taurocholate solutions with or without 0.6 mol NaCl dm−3. The ground and first excited singlet states solubilize only in the aggregates formed by sodium taurocholate, whereas the first triplet state solubilizes both in the bulk phase and in the aggregates. A lower limit of the corresponding entry and exit rate constants ke and ks, respectively has been estimated: ke ≥ 5 X 106 dm3 mol−1 s−1 (2x107 dm3 mol−1 s−1 with 0.6 mol NaCl dm−3) and ks ≥ 105 s−1. The triplet state as well as the semioxidized radical react with the taurocholate anion. The former reaction leads to the formation of semireduced dye. The latter is responsible for the detection of only semioxidized radicals which move freely in the aqueous phase. The results are compared with those obtained previously in aqueous sodium dodecyl sulphate solutions and the possible biological implication is discussed.