| Abstract: | The influence of temperature (77–230 K) on the fate of pyrene (Py) radical ions and Py excited states in irradiated poly(dimethylsiloxane) (PDMS) doped with Py is described. At 77 K, the Py radical ions seem to be stable, whereas the Py excited states [fluorescence (λ = 395 nm) and phosphorescence (λ = 575–650 nm)] are generated via tunneling charge transfer. In the range of the glass‐transition temperature (Tg = 152–153 K), the Py radical ions start to decay, taking part in a recombination process and leading to the Py monomer and Py excimer fluorescence (λ = 475 nm). The wavelength‐selected radiothermoluminescence (WS RTL) observed at approximately 395, 475, and 600 nm has helped us to identify the Tg range (152–153 K). The absorption maximum at approximately 404 nm, found in the temperature range under consideration, is thought to represent PyH?, cyclohexadienyl‐type radicals produced as a result of the reaction of Py?? with protonated PDMS macromolecules. With the initial‐rise method of evaluating the activation energy (Ea) with the WS RTL peaks observed in the Tg range, Ea values of 123–151 kJ mol?1 have been found. Such high Ea values can be explained by the contribution of energy connected to the molecular relaxation of the matrix in the Tg range. The well‐known Williams–Landel–Ferry equation, with universal constants C1 = 17.4 and C2 = 12.7, has been successfully applied to the interpretation of old pulse‐radiolysis/viscosity data found for crosslinked PDMS doped with Py. The mechanisms involved in these phenomena are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6125–6133, 2004 |
