Evidence of conjugation length distributions in electroluminescent segmented PPV: absorption, photoluminescence and Raman scattering

We present a joint experimental and theoretical analysis of the absorption, Raman scattering and photoluminescence of a segmented poly(paraphenylene vinylene) film used as active layer in a light emitting diode. In this particular polymer the experimental photoluminescence spectra are strongly dependent on the excitation energy. A model is introduced which allows the calculation of the photoluminescence spectra, based on the distribution of the conjugated segments in the polymeric chains. The calculated spectra reproduce very well the experimental data by taking into account the migration of the excitations from short to long segments whose distribution is that obtained to simulate the absorption and Raman scattering bands. The variations in the spectra observed by changing the excitation energy are well described by properly weighting the longest conjugation segments in the distribution, from where the radiative recombination begins.