Triplet Excimer of TIPS-Anthracene in Solution

Abstract Triplet excitons possess unique characteristics of long lifetimes and fission (singlet fission, SF)–fusion (triplet–triplet annihilation, TTA) features and hence have attracted considerable attention. Because the singlet–triplet transition is spin forbidden, leading to triplet states being optically “dark”, the investigation of triplet features is usually not easy. The existence of triplet excimer-like excited states (T1 + S0) has been debated over the past four decades. Among TTA and SF materials, bis[(triisopropylsilyl)ethynyl]anthracene (TIPS-Ac) is a prominent candidate since its highly efficient TTA has been demonstrated. However, because photophysical studies of TIPS-Ac are relatively nascent, its characteristics have remained elusive. Herein, we shed light on a novel feature of a triplet related excited state, which we assign as a triplet excimer of TIPS-Ac, in solution using pump–probe transient absorption (TA). This triplet excimer feature in the TA spectrum is observed as a photoinduced absorption (PIA) peak at around 700 nm, following isolated triplet PIA, with triplet sensitization and triplet generation via bimolecular interaction converting singlet to triplet excitons (e.g., SF). Moreover, the kinetics of TTA with the triplet sensitized TIPS-Ac in solution, combined with the triplet excimer feature, suggests that dissociation of the triplet excimer reproduces isolated triplets (T1) at room temperature, allowing for a longer existence of triplet excitons in the system by circumventing the consumption of triplet excitons via TTA (viz., triplet reservoir effects), which could be useful for the long-distance transportation of triplet excitons. This work provides valuable guidance for further advancement of the triplet related reactions, including TTA, SF, and beyond.