The Development of Zeolite-Entrapped Organized Molecular Assemblies

A brief summary is presented of the development of organized molecular assemblies entrapped within the supercages of Y‐zeolite. Emphasis is placed on work originating in the author's laboratory, although a discussion of some of the important contributions made by other workers, which inspired and facilitated this work, are included. Following pioneering studies by Lunsford and co‐workers, which demonstrated the feasibility of encapsulating the common photosensitizer [Ru(bpy)3]2+ within the Y‐zeolite supercage, Dutta and co‐workers documented efficient photoinduced electron transfer to viologen acceptors occupying neighboring supercages. We have extended the range of available materials by developing synthetically versatile methods to permit the incorporation of heteroleptic complexes, including constituent ligands which contain peripheral nitrogen donor groups; for example, 2,2′‐bipyrazine. In an impressive study employing zeolite‐excluded acceptors, Dutta and co‐workers showed that the reducing equivalents available from photoinduced electron transfer from the zeolite entrapped sensitizer to intra‐zeolite acceptors could be transferred to the extra‐zeolite acceptors in aqueous suspensions, although the net charge‐separation efficiency was low, presumably because of a persistent relatively efficient back‐electron transfer process involving the primary photoproduct; that is, the entrapped sensitizer–acceptor dyad. Exploiting the susceptibility of certain heteroleptic complexes to add reactive ruthenium reagents, methods were developed to construct spatially organized donor–sensitizer–acceptor triads within the supercage framework of Y‐zeolite. Such assemblies exhibit dramatically improved net charge‐separation efficiencies, presumably as a consequence of inhibiting the wasteful back‐electron transfer reaction between the initial sensitizer–acceptor couple.