Geminate and Nongeminate Recombination of Triplet Excitons Formed by Singlet Fission

We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV.