Excited state spectral and dynamics studies of MEH-PPV

Femtosecond spectroscopy studies of several thin conjugated polymer films a nd solutions were performed in order to examine the gain/loss in the excite d state. The excited state shows bimolecular interaction at distances highe r than 10 nm between excitations. The ultrafast dynamics are consistent wit h bimolecular dipole-diplole interaction, but a quantum delocalization of a t least 5 nm has to be assumed. We show how the photoinduced absorption aff ects the emission of light in long as opposed to short (thin film) optical path configurations: the photoluminescence from thick sample spectrally ove rlaps the net gain (stimulated emission minus photoinduced absorption). The results show that the observed spectral narrowing occurs through amplified spontaneous emission.