A fluorescence probe, inserted in a solid polymeric matrix, is used to follow the first steps of photo-degradation by fluorescence spectroscopy. The competition between cross-linking and chain breaking during the degradation entail physical modifications in the macromolecular chains. These modifications usually followed by gel permeation spectroscopy can be studied by extrinsic florescence spectroscopy. Due to the high sensitivity of the fluorescent probe to the polymer matrix evolution, all the structural modifications can be investigated. In particular during the first photo-degradation steps, a correlation with activation energy necessary to the chain mobility is used to understand the sensibility of the fluorescent probe. (C) 2013 Elsevier B. V. All rights reserved.