INTRAZEOLITE PHOTOCHEMISTRY .15. INFLUENCE OF AGING, INERT-GASES, ANDWATER ON THE MOBILITY OF PYRENE MOLECULES ON THE FAUJASITE NAY

The mobility and location of pyrene within the cavities of the faujasi te NaY have been examined using fluorescence and diffuse reflectance t echniques. The photophysical properties of pyrene within the zeolite f ramework show that upon incorporation the pyrene molecules are initial ly distributed in the outer cavities of the zeolite granules, This lea ds to a high number of doubly occupied cavities and large excimer emis sion; this emission shows only 20-25 ps delay, suggesting that excimer -forming molecules are required to undergo only small intracavity moti ons. With time (days) the distribution of pyrene within the cavities o f the zeolite equilibrates and monomer emission dominates the spectra. The time required for this equilibration to take place is shown to be highly dependent on sample preparation. In particular, water and hexa ne hinder pyrene redistribution, while this process is faster under ni trogen than in samples under vacuum. The detection of delayed fluoresc ence on the microsecond time scale on freshly prepared samples indicat es that there is movement of the pyrene molecules located on the exter nal surface of the zeolite after sample preparation; no delayed fluore scence is observed after 1-2 days.