ZEOLITE SENSITIZED PHOTOELECTRON TRANSFER - MODULATION OF REDUCTION POTENTIALS

The remarkable efficiency of conversion of light to chemical energy ob served in green plant photosynthesis arises due to the spatial positio ning of the sensitizers and the molecules involved in the electron rel ay. The architecture of zeolite cages also allows for positioning of m olecules spatially, and in a primitive sense mimics photosynthesis. Us ing entrapped Ru(bpy)(3)(2+) as sensitizer, directional electron trans fer to propylviologen sulfonate (PVS) in solution is possible if the m ediating viologen in the zeolite has the appropriate reduction potenti al e.g. N,N'-tetramethylene-2,2'bipyridinium (DQ(2+)). Th, reduction p otentials of viologens is controlled by introducing steric effects in the molecule such that planarity of the two bipyridyl rings upon one-e lectron reduction is difficult to achieve. We show that by using violo gen molecules that span several supercages of a zeolite e.g. benzylvio logen (BV2+), we can also alter the reduction potential, but because o f the steric constraints imposed by the zeolite framework. Thus, in th is example, not only does the zeolite provide spatial orientation, but also modulates the reduction potential of the encapsulated viologen.