MAGNETIC FIELD EFFECTS ON REACTION YIELDS IN THE SOLID STATE: An Example from Photosynthetic Reaction Centers

Magnetic Field Effects Prior to 1970 there were several reports of the effects of magnetic fields on chemical reactions, though there was much rebuttal and retraction in this early literature (1-3). Since 1970, the number of reproducible examples has grown rapidly. Most contemporary theories explaining these effects stem from the development of the radical pair theory of Chemically Induced Dynamic Nuclear Polarization, CIDNP (4, 5). These are based on the interconversion of spin multiplets through the action of inhomogeneous magnetic fields, hyperfine interactions, or differences in the g factors of the chemical species involved. Most systems that exhibit magnetic field effects involve reactions of radical pairs, though other examples, such as the interconversion of ortho and para hydrogen (3), luminescence arising from triplet-triplet annihilation (6), and quenching of triplet states by radicals (7), are well documented. A good example of the effect of a magnetic field on a reaction involving radical pairs in solution is the pioneering work by Schulten & Weller and Michel-Beyerle & Haberkorn on triplets formed by the recombination reaction between pyrene anions (2py7) and dimethylanaline cations (ZDma .+) (8-13) shown in Figure 1. Applied magnetic fields decrease the