Role of the structure on the photo and cathodo-luminescence of poly(ethylene naphthalate): PEN

The photoluminescence in the blue emission band at 430 nm of poly(ethylene naphthalate), assigned in literature to the formation of excimers states involving the naphthalene groups, is shown to be very sensitive to the disorder induced by irradiations. The cathodoluminescence, excited by a beam of 4 keV electrons, exhibits two components: a rapidly decreasing fluorescence at 430 nm and a broad and more stable one at 640 nm assigned to short chain segments. The influence of mechanical stretching and temperature on the fluorescence of non-treated PEN films has been investigated. The enhancement of the fluorescence with film elongation is attributed to the increase of the polymer chain ordering along the stretching direction, whereas the decrease of the fluorescence with temperature is correlated to the β∗ relaxation associated in dielectric spectroscopy to the movements of the naphthalene groups, known to be responsible for the excimer fluorescence. The dependence of the blue and red fluorescence components on the polymer structural organization provides efficient probes to study the local order and degradation stage of PEN and accounts for the results reported in literature according to the different film histories.