Distinct contiguous versus separated triplet-pair multiexcitons in an intramolecular singlet fission chromophore

We show from many-body quantum mechanical calculations that there occur structurally distinct triplet-pair eigenstates in the intramolecular singlet fission (iSF) compound pentacene-tetracene-pentacene. Triplet excitons occupy neigboring pentacene and tetracene monomers in the higher energy doubly degenerate triplet-triplet multiexcitons, and terminal pentacene chromophores in the lower energy multiexciton. The lowest energy multiexciton is reached by ultrafast triplet migration within the triplet-triplet manifold, a result with profound implication for the design of superior iSF compounds.