Photoelectron Transfer in Zeolite Cages and Its Relevance to Solar Energy Conversion

The cages and channels of aluminosilicate zeolites provide a novel environment for molecular and nanoparticle assembly for photochemical reactions. In their dehydrated forms, zeolites can be active participants in reactions with photoexcited entrapped molecules as electron donors and acceptors. The charge-separated species thus formed are stabilized for hours. With hydrated zeolites, the encapsulation and the restricted mobility can result in long-lived charge-separated species. In order to exploit intrazeolitic photoelectron transfer, the role of structural defects, steric effects, electrostatic polarizing fields, and extraframework cations in formation and stabilization of charge-separated species needs to be better elucidated. Such efforts will be facilitated with better control of synthesis of molecular and nanoparticle assemblies within the zeolite, rather than the random distribution mostly practiced to date. Artificial photosynthetic assemblies within zeolites aimed toward practical photolytic water splitting have potential because of varied ways of charge transport, including via the framework or molecules, as well as the synthesis of zeolite membranes that can propagate light, cations, and electrons over macroscopic distances. Assembly of catalysts capable of multielectron/hole processes within and at zeolite interfaces needs to be coupled with photochemical systems. Better integration strategies for combining efficient light collection, directed charge separation/propagation, and catalysis are necessary for practical impact.