Nonclassical 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 interphoton time distributions, second order correlation functions, and the variance of the photon number probability distribution. Antibunching at short times and bunching behavior for longer times is observed, associated with sub- and super-Poissonian statistics, respectively. A rate-equation analysis of the molecular level populations indicates an accelerated reverse intersystem crossing.