Laser flash photolysis of a series of substituted styrenes embedded within the cavities of the large pore zeolite NaY leads to the formation of the corresponding styrene radical cation. The reactivity and spectra of these radical cations embedded within NaY are examined and compared to the reactivity of the same radical cations in solution. It is found that for the highly reactive parent styrene radical cation the zeolite framework provides a strong stabilizing effect. For the 4-methoxy-substituted styrene radical cation the zeolite framework plays less of a role in stabilizing the radical cation as compared to the reactivity of the same radical cation in acetonitrile solution. Rigorous analysis of the thermal stability of 4-methoxystyrene, 4-methylstyrene, and anethole in the zeolite micropores was carried out using two sources of NaY zeolite (Aldrich and The PQ Corporation). It was found that the thermal stability was surprisingly dependent on the source of the NaY zeolite. 4-Methoxystyrene, 4-methylstyrene, and anethole were thermally stable in NaY (Aldrich) but rapidly dimerized in NaY (PQ) upon incorporation with dichloromethane. We observed the formation of the same type of dimers not only for 4-methoxystyrene but also for 4-methylstyrene and anethole. In addition, 4-methoxystyrene was incorporated into a series of different acid zeolites (HZSM-5, HMordenite, HBeta, and HY) varying in the shape and size of their micropores where rapid thermal protonation occurs. Dimerization of the thermally formed 4-methoxyphenethyl cation with a neutral molecule of 4-methoxystyrene took place within all the acid zeolites examined. The generation of this secondary 1,3-bis(4-methoxyphenyl)-1-butylium ion was clearly observed in the medium pore ZSM-5. This carbocation was found to be thermally unstable in the acidic environment provided by the four acidic zeolites and underwent a proton and hydride transfer to form the more stable allylic 1,3-bis(4-methoxyphenyl)buten-1-ylium cation. In the large round cavities of HY a competing cyclization reaction took place which led to the formation of the 3-methyl-5-methoxy-1,4-methoxyphenylindanyl cation.

The mobility and location of pyrene within the cavities of the faujasite NaY have been examined using fluorescence and diffuse reflectance techniques. The photophysical properties of pyrene within the zeolite framework show that upon incorporation the pyrene molecules are initially distributed in the outer cavities of the zeolite granules. This leads to a high number of doubly occupied cavities and large excimer emission; this emission shows only 20-25 ps delay, suggesting that excimer-forming molecules are required to undergo only small intracavity motions. With time (days) the distribution of pyrene within the cavities of 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 hexane hinder pyrene redistribution, while this process is faster under nitrogen than in samples under vacuum. The detection of delayed fluorescence on the microsecond time scale on freshly prepared samples indicates that there is movement of the pyrene molecules located on the external surface of the zeolite after sample preparation; no delayed fluorescence is observed after 1-2 days.