Study of Spectroscopic and Photochemical Behavior of Zeolite Supramolecules

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In order to elucidate the spectroscopic and photochemical behavior of guest molecules included in zeolite nanocavities, we (1) took the spectroscopic measurements of the BrΦnsted and Lewis acidities in the cavities, and studied (2) the dark reaction of aromatic alkenes caused by the BrΦnsted and Lewis acid sites, (3) the effects of alkali-metal cations in the cavities on the cis-trans photoisomerization of stilbene and azobenzene, and (4) the effects of alkali-metal cations in the cavities on the photooxygenation of aromatic alkenes. From these investigations, we obtained the following significant information about the cavities:1. Using 2-quinolone as a probe, the BrФnsted and Lewis acidities in the cavities were determined more precisely than by previous procedures such as the Hammett method.2. When electron-rich aromatic alkenes were adsorbed in proton-exchanged zeolites, their dark reaction proceeded readily due to the BrΦnsted and Lewis acid sites in the cavities. Therefore, it seems likely that alkali-metal cation exchanged zeolites are suitable photochemical reaction vessels for the alkenes.3. It was found that the co-adsorbed water in the cavities accelerated the above dark reactions.4. Due to the electrostatic interaction between guest molecules and metal cations in the cavities, the photodimerization of styrenes and the intramolecular cycloaddition of stilbenes were suppressed. As a result, the photooxygenation of the alkenes occurred more efficiently in the cavities than in solutions.5. It was found that the photochemical behavior of guest molecules adsorbed in the cavities depends on the site in which the molecules electrostatically interact with the metal cations.These results clearly indicate that the characteristics of zeolite cavities can be explained to regulate the photochemical behavior of guest molecules.