Triplet-excited dye molecules (eosine and methylene blue) quenching by H2O2 in aqueous solutions

The quenching of the triplet-excited dyes eosine and methylene blue (MB) by H2O2 has been studied by laser and steady-state photolysis. The quenching rate constant of the eosine triplet is k(q) = 2.4 +/- 0.3 x 10(5) (M s)(-1) and rate constant of MB quenching with H2O2 was found to be k(q) = 6.5 +/- 0.5 x 10(5) (M s)(-1). The decolorization of both dyes is accelerated upon H2O2 addition under steady-state photolysis and the redox reaction mechanism is suggested. The quantum yield for ion-radicals formation obtained were: for eosine 0.01 +/- 0.005 and 0.03 +/- 0.01 for MB. This latter observation provides the evidence for stability of these dyes under light irradiation in the presence of H2O2. (C) 1998 Elsevier Science S.A. All rights reserved.