Recent research of external magnetic field effects (MFE) on chemical reactions is reviewed. The triplet radical pair which is generated by photo reactions can not take place back electron transfer or recombination reaction by a spin parity rule, and only take place them via singlet state after intersystem crossing. The magnetic fields affect the intersystem crossing rate between triplet and singlet states of the radical pair, and the yield of reaction products will be affected by the magnetic field. Several mechanisms, (a) Δg mechanism, (b) HFC mechanism, and (c) spin relaxation mechanism, for the effects on photoreactions have been proposed. The roles of these mechanisms for chemical reactions are described.

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The porphyrins we have touched with so far are naturally occurring, and are involved in the light-harvesting reactions of photosynthesis and the storage functions of cellular metabolism. Synthetic porphyrins are already being tried out in laboratories around the world in a wide variety of applications, including medicine, electronics, and alternative energy generation. Given the importance of these processes, it is not surprising that understanding photosynthesis has long been a major research priority for chemists and engineers involved in nanotechnology. Electron Transfer (ET) reactions play a central role in photosynthesis. In order to obtain a better understanding of the exact nature of specific partner-to-partner ET processes and to be able to duplicate them in vitro, the research has focused on the more complicated “supramolecular” model systems derived from porphyrin. In the light of the previous studies, the roles of non-covalent pathways in mediating long-range ET reactions were studied. Multi-component arrays with improves charge separating capabilities were prepared, and these species may find applications in new charge separating devices. This review summarizes our recent progress in this rapidly growing field.

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