PHOTOPHYSICAL PROPERTIES OF PYRENE IN ZEOLITES .2. EFFECTS OF COADSORBED WATER

The effects of coadsorbed water, following pyrene adsorption, on oxygen and Tl+ and perylene quenching of pyrene fluorescence in zeolite A and zeolite X have been examined. For zeolite X, coadsorbed water drastically decreases the oxygen-quenching efficiency but enhances the Tl+ quenching of pyrene fluorescence. On the other hand, coadsorbed water does not affect the energy-transfer quenching between 1pyrene* and perylene. In both hydrated and dehydrated zeolite X samples, Tl+ quenches 1pyrene* via an electron-tunneling mechanism. We have determined the active radius for the hydrated and dehydrated zeolite X samples to be 16.0 ± 1.6 and 11.1 ± 1.0 A, respectively. The perylene quenching of 1pyrene* in zeolite X follows a Forster dipole-dipole interaction mechanism with a critical transfer distance of 38.9 ± 3.0 A for hydrated samples and of 37.6 ± 1.4 A for dehydrated samples. For zeolite A, coadsorbed water does not block oxygen quenching of 1pyrene*, which requires close contact of reactants. In addition, T1+ ions do not quench 1pyrene* in zeolite A under any conditions stated above. Pyrene is adsorbed at the surface of zeolite A, giving ready access to oxygen, while T1+ ions are adsorbed in the zeolite pores at same distance from pyrene. © 1990, American Chemical Society. All rights reserved.