Bulk fluorescence measurements cannot probe the survival-time distribution of single molecules

Using a straightforward theoretical approach, we show that an ensemble of dyes with a simple first-order photobleaching kinetics yields a power-law decaying emission intensity in a heterogeneous excitation field in bulk fluorescence experiments. Our theoretical considerations are experimentally confirmed for two distinct classes of small organic fluorophores represented by the classical laser dye rhodamine-6G on glass in air and the cyanine dye DiI(C18) in a thin polymethylmethacrylate film. Our results provide evidence that the time course of bleaching in a bulk sample in general does not allow derivation of the properties of survival times of individual quantum systems.