The development of zeolite-entrapped organized molecular assemblies

A brief summary is presented of the development of organized molecular asse mblies 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 fa cilitated this work, are included. Following pioneering studies by Lunsford and co-workers, which demonstrated the feasibility of encapsulating the co mmon photosensitizer [Ru(bpy)(3)](2+) within the Y-zeolite supercage, Dutta and co-workers documented efficient photoinduced electron transfer to viol ogen accepters occupying neighboring supercages. We have extended the range of available materials by developing synthetically versatile methods to pe rmit the incorporation of heteroleptic complexes, including con stituent li gands which contain peripheral nitrogen donor groups; for example, 2,2'-bip yrazine. In an impressive study employing zeolite-excluded accepters, Dutta and co-workers showed that the reducing equivalents available from photoin duced electron transfer from the zeolite entrapped sensitizer to intra-zeol ite accepters could be transferred to the extra-zeolite accepters in aqueou s suspensions, although the net charge-separation efficiency was low, presu mably because of a persistent relatively efficient back-electron transfer p rocess involving the primary photoproduct; that is, the entrapped sensitize r - acceptor dyad. Exploiting the susceptibility of certain heteroleptic co mplexes to add reactive ruthenium reagents, methods were developed to const ruct spatially organized donor-sensitizer-acceptor triads within the superc age framework of Y-zeorite. Such assemblies exhibit dramatically improved n et charge-separation efficiencies, presumably as a consequence of inhibitin g the wasteful back-electron transfer reaction between the initial sensitiz er - acceptor couple.