Intramolecular relaxation processes of benzophenone and related molecules in glassy media

Abstract

Radiofrequency (10²–10⁵ Hz), variable temperature (77–333 K) dielectric loss measurements were performed for a series of diaryl ketones and pyridyl ethylenes in polystyrene, and in the case of benzophenone and 2,3,4,5,6-pentadeuterobenzophenone also in o-terphenyl and in Santovac {bis[m(m-phenoxy phenoxy)phenyl]ether}. An intramolecular process with a low enthalpy of activation (ΔH_E≈ 20 kJ mol^–1) was observed in the benzophenones and ΔH_E≈ 30 kJ mol^–1 for bis(2-pyridyl) ketone and 1,2-bis(2- and 4-pyridyl) ethylene. A mesomeric process would seem to be the most probable intramolecular mechanism through which these symmetrically substituted ketone and ethylene derivatives relax. The observed relaxation processes seem to be unaffected by varying the medium.