Intrazeolite photochemistry .19. Effect of the ''spectator'' pyridine on the behavior of carbonyl triplet states in the zeolite NaY

''Spectator'' molecules, which do not participate directly in the photochemistry of organic molecules included in zeolites, can be used to ''tune'' their photochemistry and photophysics. Such control can be exerted through changes in the diffusional behavior, spatial restrictions, or modification of the acid-base properties of the zeolite, in the case of the faujasite NaY, we have employed pyridine as a ''spectator'' to alter the behavior of xanthone, p-methoxy-beta-phenylpropiophenone, and benzophenone which provide examples of the three mechanisms mentioned above. These processes were examined with laser flash photolysis techniques employing diffuse reflectance detection. For example, the lifetime of triplet xanthone is enhanced nearly 2 orders of magnitude when a small amount of pyridine is included, showing that a small number of acid sites in NaY may severely quench the excited triplet. in the case of p-methoxy-beta-phenylpropiophenone, incorporation of large concentrations of pyridine restricts the motions required for beta-phenyl intramolecular quenching and leads to an increase in triplet lifetime.