Measurement of magnetic field effects on radical recombination reactions using triplet–triplet energy transfer

Previously, the effect of applied magnetic fields on the yield of the reaction of the radical ions of pyrene and 1,3-dicyanobenzene (DCB) has been measured by monitoring the emission of the pyrene/1,3-DCB exciplex formed from the singlet state of the spin-correlated radical pair (SCRP). This Letter describes an alternative approach that relies on energy transfer from the excited triplet state of pyrene to the tris(2,2′-bipyridyl)ruthenium(II) ion, Ru ( bpy ) 3 2 + , allowing the recombination of the triplet SCRP to be monitored by emission spectroscopy. Measurements of magnetic field effects in combination with time-resolved flash photolysis and luminescence experiments confirm triplet–triplet energy transfer as the reaction mechanism.