Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract In this article, we illustrate how one can utilize the cation embedded in a zeolite matrix to control the photophysical and photochemical behavior of guest molecules included in zeolite cages/cavities. Three aspects of cation-guest interaction are highlighted. Strong electronic interaction between the cation and the guest leads to mobilization of guests within zeolite supercages, alteration of the lowest electronic configuration (nл*, лл*) and restriction of conformation of molecules. Less obvious to a non-photochemist is the ability of cations, depending on their atomic weight, to induce spin conversion (singlet-triplet) in molecules. Photophysical studies carried out with aromatics and photodimerization of acenaphthylene highlight this point. The power of the heavy-atom cation effect in zeolites has been demonstrated by recording phosphorescence from several olefins whose phosphorescence has not previously been recorded. Cations by their sheer size can influence the mobility of molecules within zeolites. Restriction of motion of reactive intermediates results in product selectivity in reactions as illustrated with a few examples. Properties of cations and consequently their influence can change depending on whether they are hydrated or uncoordinated to water. Aggregation of dyes and aromatics and reactivities of carbonyl compounds are influenced by water present within zeolites. We have shown in this article that zeolites can be used as unique reaction vessels for photochemical reactions.
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