MOLECULAR-STRUCTURES OF PORPHYRIN-QUINONE MODELS FOR ELECTRON-TRANSFER

Synthetic porphyrin-quinone complexes are commonly used to mimic elect ron transport in photosynthetic reaction centers and to probe the effe cts of energetics, distances, and relative orientations on rates of el ectron transfer between donor-acceptor couples. The structures of two such models have been determined by X-ray diffraction. The redox pairs consist of a zinc porphyrin covalently linked to benzoquinone in cis and trans configurations via a cyclohexanediyl bridge. The crystallogr aphic studies were undertaken to provide a structural foundation for t he extensive body of experimental and theoretical results that exists for these compounds in both the ground and photoinduced charge-separat ed states. The results validate conclusions reached from theoretical c alculations, EPR and two-dimensional NMR results for these states.