Dissociation of triplet pair states in intramolecular singlet fission materials*

We have recently demonstrated efficient intramolecular singlet fission (iSF) materials that achieve multiple exciton generation in isolated (i.e., in dilute solution) polymers and small molecules with multichromophore character. In these materials, singlet fission is a two-step process in which photoexcited singlet excitons rapidly decay into triplet pair states with strong exchange coupling (multiexciton), followed by dissociation into free triplets. Still, fundamental questions concerning the electronic and mechanistic requirements that drive both the formation and decay of the triplet pair state remain. Using correlated ultrafast optical and electron spin resonance measurements, we identify long lived triplet pairs that exist in net singlet and quintet spin multiplicities. By exploiting both intra- and intermolecular interfacial interactions, we are able to promote the dissociation of triplet pairs into free triplets. These studies establish the efficacy of iSF compounds as viable candidates for singlet fission based optoelectronic devices.