Photon statistics in single-molecule fluorescence at room temperature

The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of inter-photon time distribution, second-order correlation function, and Mandelʹs Q-function. Nonclassical photon statistics is observed and a reverse intersystem crossing is detected that accelerates linearly with the applied laser power. Rate equations for the time evolution of the molecular level populations are shown to be appropriate for the analysis of the observations.