Magnetic field effects on the decay rates of photogenerated geminate radical pairs in reversed micelles

Abstract

Laser excitation (351 nm) of zinc tetraphenylporphinate-viologen pairs in reversed micelles (AOT/isooctane or n-hexane) afforded triplet radical pairs in a cage, and the decay was remarkably retarded in external magnetic fields (0-1 T). In the case of the porphyrin-viologen linked compound, the radical decay rate decreased by an order of magnitude to reach a plateau region at above 0.3 T. Exactly the same behavior was also observed with nonlinked porphyrin-viologen pairs, which consisted of amphiphilic or cationic porphyrin and a zwitterionic viologen, in a small water pool (ca. 10 {angstrom} in radius) of the reversed micelles. The large external magnetic field effects on the linked (or pseudolinked) radical pairs were explained on the basis of Zeeman splitting of the triplet in combination with electron spin relaxation from the sublevels (relaxation mechanism), and supporting evidence was provided by the use of paramagnetic lanthanide ions.