Zeolite-based organized molecular assemblies and their application to photochemical storage of light energy

An intense interest and activity in studies of Ru(bpy)$\sb3\sp{2+}$ and related complexes has been sustained for over two decades because of their utility in addressing many fundamental photochemical and photophysical issues and, more importantly, because of their potential value as useful components in practical solar energy conversion devices. In this work the fundamental issues as well as the practical applications of Ru(II)-polypyridine complexes as components of the Y-zeolite based photocatalytic systems are investigated. A series of complexes, Ru(bpz)$\rm\sb2L\sp{2+},$ was prepared wherein the donor strength of the spectator ligand, L, was varied in a systematic manner. Analysis of excited state lifetime data, acquired over wide range of temperatures, revealed a quantitative dependence of the relative importance of two competing thermally activated decay pathways on the donor strength of the spectator ligand. The nature and extent of interactions between Ru(bpy)$\sb3\sp{2+}$ molecules entrapped within the supercages of Y-zeolite have been studied by employing a series of zeolitic samples with different loads of the entrapped complex. Analysis of lifetime measurements as a function of concentration and power revealed the effect of interactions of the excited state *Ru(bpy)$\sb3\sp{2+}$ with both ground and excited state species in adjacent cages. A novel method for the construction of zeolite entrapped molecular assemblies, in which two different Ru(II)-polypyridine complexes are immobilized in adjacent supercages of Y-zeolite, has been developed. The two complexes forming the assembly are chosen so that one of them can act as photosensitizer and one as an electron donor. Spectroscopic studies suggest that the synthetic method developed is efficient in forming adjacent cage assemblies and that the entrapped complexes are strongly coupled with respect to electron transfer. The applicability of the above mentioned zeolite entrapped molecular assemblies to the photochemical storage of light energy has been investigated. Photoredox studies of system comprised of donor (Z-Ru(mmb)$\sb3\sp{2+})$:sensitizer (Z-Ru(bpy)$\sb2$bpz$\sp{2+})$:relay (diquat) and extrazeolitic acceptor (propylviologen sulfonate), have shown that a significant improvement in net charge separation efficiency can be attained for the adjacent cage assemblies relative to a simple reference system