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)32+, 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.