Triplet-Triplet Annihilation via the Triplet Channel in Crystalline 9,10-Diphenylanthracene.

Delayed fluorescence resulting from triplet-triplet annihilation in crystalline 9,10-diphenylanthracene was observed by means of steady-state fluorescence measurements under magnetic fields of ≤10 T. At five specific magnetic fields, four peaks and one dip in the magnetic field dependence of fluorescence intensity were observed, proving that exchange-coupled triplet pairs were generated in the course of triplet-triplet annihilation. The dip was in the opposite direction predicted for singlet channel triplet-triplet annihilation. Further analysis using the stochastic Liouville equation confirmed that the closest exchange-coupled triplet pair in crystalline 9,10-diphenylanthracene is quenched via both triplet channel and singlet channel triplet-triplet annihilation.