Long Lifetime Delayed Fluorescent Materials with Water and Temperature Tolerability Based on Charge Separation States

Abstract Long lifetime delayed fluorescent materials have great potential applications in bioimaging, anti‐counterfeiting encryption, lighting, and other fields. However, the preparation of functionalized long lifetime fluorescent materials with simple chemical structure and tunable luminescent behavior still poses significant challenges. In this article, a simple and effective method to prepare a series of long lifetime delayed fluorescent copolymers with temperature and humidity tolerance is presented. This method involves the copolymerization of 2‐bromo‐5‐hydroxybenzaldehyde derivative monomer (M1), which contains electron‐withdrawing groups, with naphthalimide derivative fluorescent monomer (M2), which contains electron‐donating groups. The results demonstrate that long‐range charge transfer occurs between the two components in copolymers, forming charge‐separated states that emit long lifetime delayed fluorescence after exciton recombination. The delayed luminescent behavior of the copolymer is directly influenced by the content of the M2 component. The maximum delayed fluorescence lifetime can reach 13.7 ms, and the fluorescence quantum yield is 39%. Interestingly, the polymer film of P3 can emit a maximum afterglow of 1.00 s after photoactivation. Even after being immersed in water for 49 days, the afterglow remains unchanged. Besides, the afterglow of P3 can exist for ≈0.43 s at 323 K. Even at 373 K, the afterglow for 0.2 s can still be observed.