Lastly the sample 1,4-PDA, as in the static measures, shows only a broadband emission which presents a decay characterized by a late rise in the intensity (about 1000 ns) followed by a long decay over tens of s. This could be an indication of a complete and efficient energy transfer from the higher energy free exciton to a red-shifted self-trapped exciton with an efficient radiative recombination mechanism. Consistently this sample has the highest ΔE (ΔE1,4-PDA=95meV) between the analyzed samples leading to a photoluminescence dominated by radiative recombination of carriers both at room and cryogenic temperature. The late rise in PL intensity suggests a back transfer mechanism from the non-radiative recombination sites to the radiative one; this feature is not present in 1,3-PDA decay which emission is, in fact, dominated by non-radiative pathways, from which a back transfer to the radiative state is hindered.