Deep‐Blue Delayed Fluorescence Supramolecular Assembly with Ultrahigh Quantum Yields of 81% from an Extraordinary Source of π–π* Transition

Abstract Blue/deep‐blue emission is an essential core element for application in organic optoelectronics, but it remains an enormous challenge in organic afterglow owing to the difficulties in the stabilization of the high‐lying triplet excited state. Here, an effective approach to develop a deep‐blue delayed fluorescence (DF) supramolecular assembly with long lifetime and record‐high quantum efficiency up to 0.62 s and 81%, respectively, is proposed via the increase in the delocalization degree of guest molecules induced by the co‐assembly of guest molecules with Laponite (Lap) achieved via simple solvent‐free grinding approach. Thereby the excitation energy of singlet excited states of π–π* transition (S₁ (¹(π, π*))) decreases, making the π–π* transition of CC bonds as the main intersystem crossing (ISC) pathway from S₁ to triplet excited states (T₁) dominate the blue DF spectrum. Surprisingly, (TPA)_n@Lap still exhibits excellent afterglow characteristics with long lifetime of 0.567–0.481 s and high quantum efficiency of 72%–41% even in aqueous environments with water content from 20% to 98%. Benefiting from the excellent property, the visual detection of Fe³⁺ in water environment and high‐level information encryption application are exhibited. These results provide an important foundation for the development of blue/deep‐blue afterglow materials with high efficiency and may inspire extensive applications in the future.