Persistent Multiexcitons from Polymers with Pendent Pentacenes

Singlet fission has emerged as a key mechanism of exciton multiplication in organic chromophores, generating two triplet excitons from a single photon. Singlet fission is typically studied in crystalline films or in isolated dimers. Here, we investigate an intermediate regime where through-space interactions mediate singlet fission and triplet pair recombination within isolated polymer chains. Specifically, we investigate how appending pentacenes to a polynorbornene backbone can lead to macromolecules that take advantage of through-space π-π interactions for fast singlet fission and rapid triplet pair dissociation. Singlet fission in these systems is affected by molecular dynamics, and triplet-triplet recombination is a geminate process where the rate of recombination scales with molecular-weight. We find that these pendent pentacene polymers yield free triplets with lifetimes that surpass those of crystalline chromophores in both solution as isolated polymers and in thin films.