Electric field (EF) induced quenching of the fluorescence of large (ca. 10(3) monomers) single chains of MEH-PPV was observed. Directly after application of the field most of the individual MEH-PPV chains were either unaffected by the field or completely quenched by it, while the number of affected molecules increased with the strength of the EF Moreover, application of the field induced fluorescence blinking. Both effects are attributed to EF-assisted formation of long-living charged species that during their lifetime act as quenchers for excitations. The same type of quenchers are thought to be responsible for blinking observed without an electric field. (c) 2005 Elsevier B.V. All rights reserved.