In fact, based on isotopic pre-equilibrium models underlying eq 10, we assume constant concentrations of 1 O 2 and 3 RB * over the course of an experiment, reactions of O 2 and 3 RB * as predominant 3 RB * quenching mechanism, as well as a constant rate of formation of 3 RB * and a constant 1 O 2 formation yield. Given that the rose bengal concentrations varied between 0.5 and 20 µM, the assumptions implied in the pre-equilibrium model are likely not strictly valid for all experimental conditions. The ensuing differences in reaction kinetics could be potential sources of the observed variations of O-AKIE values.