Exponential and power-law kinetics in single-molecule fluorescence intermittency

Perylenemonoimide chromophores, attached to a small dendron arm embedded in the polymer hosts Zeonex, poly(vinylbutyral), and poly(methyl methacrylate), are studied by means of laser-induced confocal fluorescence detection. Transient fluorescence intensity exhibits dark periods on two different time scales: on a 100,us time scale and on a considerably longer time scale, ranging from 100 ms to as much as tens of seconds under high-vacuum conditions. The exponentially distributed short off times are attributed to triplet excursions of the molecule. The long-lived dark states follow a power-law distribution and are discussed in terms of the formation of radical anions/cations via electron tunneling processes.