Characterizing the Role of Peierls Vibrations in Singlet Fission with the Adaptive Hierarchy of Pure States

Abstract: Singlet fission, a phenomenon in which a singlet exciton is converted to two triplet excitons, is sensitive to vibrations that perturb couplings between electronic states (i.e., Peierls vibrations). In singlet fission models larger than dimers, the inconvenient scaling of exact simulations has limited treatment of Peierls vibrations to approximate methods. In this letter, we generalize the formally exact, reduced-scaling adaptive Hierarchy of Pure States (adHOPS) method to account for both Holstein and Peierls vibrations and study singlet fission in N,N'-Bis(2-phenylethyl)-3,4,9,10-perylenedi-carboximide (EP-PDI). We find that Peierls vibrations accelerate singlet fission by generating correlated charge transfer-mediated pathways that support constructive interference. Finally, we extend this singlet fission model to a linear chain of EP-PDI to demonstrate that Peierls vibrations can accelerate singlet-mediated triplet transport on the 100-nm scale.