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

Abstract

To reveal the relationship between molecular packing and singlet fission (SF) property is necessary for developing efficient SF materials, yet it remains unclear. Herein, we investigated SF in two perylenediimide (PDI) films (PDI-C4 and ClPDI-C4) with different molecular arrangements. Crystal structure analysis reveals that PDI-C4 with no substituent at the bay position has a planar structure and shows a close intermolecular packing with a sufficient π-π overlap. Compared to PDI-C4, ClPDI-C4, with four chlorine groups at the bay position, exhibits a twisted core structure that prevents a close intermolecular packing and shows a small π-π overlap. This leads to a smaller intermolecular interaction in ClPDI-C4 film with respect to PDI-C4 as revealed by their steady-state absorption spectra. Transient absorption spectra demonstrate that ClPDI-C4 shows a relatively slower SF rate compared to PDI-C4, but with a longer triplet lifetime. This may be caused by the looser molecular packing and the more endothermic SF in ClPDI-C4 film. This indicates that the introduction of substituents onto the bay position of PDI may be a good choice to tune the PDI packing for achieving long-lived triplets.