Using ultrafast spectroscopy, we report evidence of monodimensional photophysics coming from isolated chains of poly(9,9-dioctylfluorene) dispersed in a polymethylmethacrylate matrix. We identify intrachain charge carriers dynamics, the decay taking place in about 1 ps. Using a three-pulse experiment we bring evidence for charges generation from higher lying states and we report an ultrafast optical gain switching in the stimulated emission region over a broad wavelength range (around 100 nm). Our experiments suggest that the expected maximum rate of on-off switching in such a molecular device can be as high as 300 GHz. © 2005 American Institute of Physics.