ZEOLITE SENSITIZED PHOTOELECTRON TRANSFER - MODULATION OF REDUCTION POTENTIALS

The remarkable efficiency of conversion of light to chemical energy observed in green plant photosynthesis arises due to the spatial positioning of the sensitizers and the molecules involved in the electron relay. The architecture of zeolite cages also allows for positioning of molecules spatially, and in a primitive sense mimics photosynthesis. Using entrapped Ru(bpy)(3)(2+) as sensitizer, directional electron transfer to propylviologen sulfonate (PVS) in solution is possible if the mediating viologen in the zeolite has the appropriate reduction potential e.g. N,N'-tetramethylene-2,2'bipyridinium (DQ(2+)). Th, reduction potentials of viologens is controlled by introducing steric effects in the molecule such that planarity of the two bipyridyl rings upon one-electron reduction is difficult to achieve. We show that by using viologen molecules that span several supercages of a zeolite e.g. benzylviologen (BV2+), we can also alter the reduction potential, but because of the steric constraints imposed by the zeolite framework. Thus, in this example, not only does the zeolite provide spatial orientation, but also modulates the reduction potential of the encapsulated viologen.