A Heavy‐atom‐free Molecular Motif Based on Symmetric Bird‐like Structured Tetraphenylenes with Room‐Temperature Phosphorescence (RTP) Afterglow over 8 s

In recent years, pure organic room‐temperature phosphorescence (RTP) with highly efficient and long‐persistent afterglow has drawn substantial awareness. Commonly, spin‐orbit coupling can be improved by introducing heavy atoms into pure‐organic molecules. However, this strategy will simultaneously increase the radiative and non‐radiative transition rate, further resulting in dramatic decreases in the excited state lifetime and afterglow duration. Here in this work, a highly symmetric bird‐like structure tetraphenylene (TeP), and its three symmetrical halogenated derivatives (TeP−F, TeP−Cl and TeP−Br) are synthesized, while their RTP properties and mechanisms are systematically investigated by both theoretical and experimental approaches. As the results, the rigid, highly twisted conformation of TeP restricts the non‐radiative processes of RTP and gives rise to the enhancement of electron‐exchange, which can contribute to the RTP radiation process. Despite the faint RTP of the bromine and chlorine‐substituted ones (TeP−Br, TeP−Cl), the fluoro‐substituted TeP−F exhibited a long phosphorescent lifetime up to 890 ms, corresponding to an extremely long RTP afterglow over 8 s, which could be incorporated into the best series of non‐heavy‐atom RTP materials reported in previous literature. Ultralong room‐temperature phosphorescence (RTP) afterglow of>8 s without heavy atoms is realized in the rigid twisted structure TeP−F. The properly promoted electron‐exchange with adequate spin‐orbit coupling enhancement and the restricted molecular motions jointly give rise to the slow but efficient RTP emission, which is a great advantage over the heavy‐atom RTP materials.