Influence of self-trapped states on the fluorescence intermittency of single molecules

We present data on photoinduced fluorescence intermittency of single terrylene molecules embedded in polymer films. Intermittency statistics follow power laws on time scales from tens of milliseconds to tens of seconds. Power law exponents vary with the polarity of the medium while the probability of long dark periods is drastically increased in the more polar matrix. Our experiments support a picture, which assumes a molecule charged by photoexcitation and coupled to a broad manifold of (charged) self-trapped states stabilized by the dielectric response of the surrounding matrix. This model is able to explain long living dark states both for semiconductor nanoparticles and fluorescent dye molecules making use of a unique microscopic description. It also takes into account a competitive photoinduced irreversible bleaching of the molecular state.