Long-Lived Triplet Radical Ion Pair State of Porphyrin-Methylviologen Combined Systems as Revealed by a Large Magnetic Field Effect on Its Lifetime

The external magnetic field effect on the lifetime of the ion pair state has been examined for the porphyrinmethylviologen combined systems in polar solvents by using nanosecond laser flash photolysis techniques. Applying the external magnetic field, a drastic increase in the lifetime has been observed. For PllMV2+ in DMSO under the magnetic field of 50 mT, the ion pair lifetime was almost three times longer than the zero field value, which can be deemed the ideal case of the external magnetic field effect due to the hyperfine interaction mechanism. The results clearly showed that the long-lived ion pair was formed by the intramolecular electron transfer from the triplet state of porphyrin.