Unveiling Excimer-like Intermediates in Singlet Fission of a Pentacene-Based Imide

Abstract

Abstract Singlet fission (SF) holds promise for enhancing photovoltaic efficiency and enabling spin-based quantum technologies. The development of new materials is hindered by the limited understanding of the SF mechanism. One particular challenge lies in the role of the excimer state, which has been proposed as a trap state that deactivates SF. Herein, we demonstrate that a novel pentacene tetraimide (PeTI) undergoes efficient SF via an excimer-like intermediate. Unlike pentacene, the benchmark SF chromophore, PeTI achieves exceptional photostability through peripheral imide functionalization. The formation of an excimer-like intermediate with spectral features characteristic of triplet states was confirmed by transient absorption and sensitization measurements. The decay of the excimer-like state in the visible and near-infrared regions coincided with efficient triplet formation, yielding a triplet quantum yield of 191%. In polystyrene matrices, this excimer-mediated dynamics was suppressed, leading to SF quenching─consistent with solution-phase behavior. Our results showed that PeTI can be used as a novel SF chromophore, and the role of the excimer state in SF needs reconsideration in future material design.