Influence of core-twisted structure on singlet fission in perylenediimide film

•Two perylenediimide (PDI) films with distinctly different intermolecular arrangements were obtained via changing the substituent onto the bay position of PDI.•Singlet fission (SF) could be conducted in these two PDI films but with different rates and triplet lifetimes.•The loose intermolecular arrangement is more favorable for achieving long-lived triplet state.•A new strategy for optimizing SF properties was proposed for developing SF materials based on PDI derivatives.