Quenching of photo-excited triplet-state anthracene through triplet-triplet (T-T) energy transfer mechanism by a few energy acceptors in the ground state, was investigated in a dehydrated Na+ form of zeolite Y (NaY) with a transient absorption spectroscopy using a diffuse reflectance detection technique. It was found that the decay curves of T-T absorption for anthracene obeyed unconventional kinetics that could be treated by a model based upon continuous time random walk theory. Analysis of the quenching kinetics offered an estimate of the intrazeolite self-diffusion coefficient for the guest aromatics. A simplified version of the continuous time random walk treatment was developed which permitted the extraction of information on diffusivity alone by analyzing the long-term tail of triplet decay signals measured using a conventional photomultiplier detection system with limited time resolution. The self-diffusion coefficients thus obtained (table 53) at 298K were significantly smaller than those observed for benzene (10-10 to 10-13m2/s). This demonstrated that the triplet quenching method was a powerful technique for evaluating diffusion coefficients of relatively large organic molecules with small intrazeolite mobility that were hardly measurable by NMR and other traditional techniques.

Triplet-Triplet Energy Transfer as a Tool for Probing Molecular Diffusivity within Zeolites. S.Hashimoto, M.Hagiri, A.V.Barzykin: Journal of Physical Chemistry B, 2002, 106[4], 844-52