ENDOR of perylene radicals adsorbed on alumina and silica-alumina powders: II. The matrix effects

Abstract

Nuclei in the environment (matrix) of perylene cation radicals formed on activated alumina and silica-alumina powders exposed to solutions of perylene in benzene solvent were probed with electron nuclear double-resonance (ENDOR) spectroscopy. Both normal and fully deuterated perylene and benzene were studied. Depending on the nature of the sample and experimental conditions, signals were detected from protons, deuterons, and aluminum-27 in the environment of the radical. A strong proton matrix signal was observed in spectra of alumina-adsorbed radicals in all preparations, indicating the presence of protons on the surface. In contrast, spectra of radicals adsorbed on silica-alumina exhibited much weaker proton matrix signals under all conditions. A deuterium matrix signal was observed with both alumina and silica-alumina surfaces (although weakly on the latter) when deuterated solvent was present. Aluminum-27 signals were seen only from samples on the alumina surface. Active site models consistent with the results are discussed. The results suggest that the radicals, although themselves similar, occupy sites of significantly different environment.