Hypermobility of Aromatic Guest Species in Zeolite as Observed from Anthracene Triplet Self-Quenching within NaY in the Presence of Critical Amounts of Coadsorbed Solvents

Abstract

The decay kinetics was investigated of triplet-state anthracene adsorbed into the cavities of a faujasite zeolite, NaY, both in the absence and in the presence of various quantities of water and other coadsorbed inert solvent molecules. It was found that at a sufficiently low loading level of anthracene the decay rate is dependent on the amount of water, methanol, and pyridine but is scarcely affected by n-hexane. When the decay rates are plotted versus the amount of solvents introduced, convex curves were obtained with a peak at ca. 0.1 cm3·g-1, which is approximately a quarter of the total pore volume of NaY (0.378 cm3·g-1). The enhanced triplet decay rate was found to be ascribable to a self-quenching event, i.e., the triplet quenching by ground-state anthracene. Thus a picture was given that anthracene molecules are highly mobile when the zeolite cavities are loaded with the coadsorbed solvents in quantities sufficient to shield the cationic sites at which anthracene is supposed to be adsorbed. The ki...