Direct exciton quenching in single molecules of MEH-PPV at 77 K

Fluorescence blinking behaviour was observed for single molecules of the conjugated polymer poly[2-methoxy,5-(2′-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) at 77 and 300 K. No strict qualitative dependence on temperature was observed, despite of the expected suppression of exciton migration at the low temperature. We assume MEH-PPV molecules to form dense nanoparticles with a characteristic size of about 10 nm at the largest. In such small nanoparticles exciton can be efficiently quenched by a photogenerated quencher due to Förster transfer just after a few hops over the polymer nanoparticle. Thus, long-distance exciton migration is not necessary to have strong fluorescence intensity fluctuations.