Ionic and excited species in irradiated poly(dimethylsiloxane) doped with pyrene

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 ( ϭ 395 nm) and phosphorescence ( ϭ 575-650 nm)] are generated via tunneling charge transfer. In the range of the glass-transition temperature (T g ϭ 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 ( ϭ 475 nm). The wavelength-selected radiothermoluminescence (WS RTL) observed at approximately 395, 475, and 600 nm has helped us to identify the T g 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 •Ϫ with protonated PDMS macromolecules. With the initial-rise method of evaluating the activation energy (E a ) with the WS RTL peaks observed in the T g range, E a values of 123-151 kJ mol Ϫ1 have been found. Such high E a values can be explained by the contribution of energy connected to the molecular relaxation of the matrix in the T g range. The well-known Williams-Landel-Ferry equation, with universal constants C 1 ϭ 17.4 and C 2 ϭ 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.

Effect of proton irradiation on photoluminescent properties of PDMS–nanodiamond composites

“…The influence of irradiation on the luminescence of polymers has been much less studied than on their optical absorption, electrical conductivity, thermal and mechanical properties [15]. The irradiation-induced changes in polymers through cross-linking, chain scission, photo-oxidation and conformational disorder can all affect their optical properties [16,17]. Luminescence properties of polymers (and polymer composites) are of potential interest for irradiation dosimetry, where the irradiation dose can be determined easily using the luminescence color and/or intensity.…”

Fluorescence spectroscopy and thermal relaxation processes of anthracenyl‐labeled polysiloxanes

“…In general, silicones are not intrinsically luminescent materials although some functionalized fluorescent silicones have been prepared 4–15. Materials with electroluminescent and semi‐conductive properties have been described in the literature 16–18.…”

“…There are different strategies to transform a nonemissive polymeric material into a luminescent system. In the simplest case, a luminescent molecule is introduced into the polymer bulk by sorption, forming a host‐guest system 7, 19, 20. The disadvantage of such extrinsically luminescent materials is that the solubility of the guest in the polymeric host is limited, and the guests can be desorbed during use.…”