High photo-stability of single molecules in an organic crystal at room temperature observed by scanning confocal optical microscopy

Single molecules have been observed in a molecular crystal at room temperat ure using scanning confocal fluorescence microscopy. Individual terrylene m olecules in a p-terphenyl crystal show high photo-stability with a correspo nding ensemble-averaged photo-destruction quantum efficiency lower than 1.2 x 10(-8). On average, with a detection efficiency of 6.5%, a stable fluore scence signal of 10(5) photons s(-1) could be detected from single molecule s during 1 min of continuous photo-excitation. Both irreversible and revers ible abrupt fluorescence intensity jumps to the background have been observ ed. The experimental data indicate that diffusing quenchers at low concentr ation in the crystal contribute to fluorescence bleaching of single molecul es. All molecular fluorescence signals follow a typical power saturation la w with a mean saturation count rate of 4.3 x 10(5) photons s(-1). The large photo-stability allows for long illumination times and high emission rates of single molecules trapped in a crystal at room temperature. A potential application as single organic quantum light sources under ambient condition s is conceivable.