TADF-type organic afterglow emitters for fabricating high-performance organic long persistent luminescence materials in difluoroboron β-diketonate systems

Organic long persistent luminescence (OLPL) materials are capable of exhibiting ultralong afterglow lasting for several hours. However, current design approaches for OLPL materials are still constrained, highlighting the need for further exploration. Here we propose a concept for building OLPL materials by thermally activated delayed fluorescence (TADF)-type organic afterglow emitters. The TADF afterglow emitter, which is a difluoroboron β-diketonate luminescent molecule (SBF₂) in this study, exhibit high molar absorptivity, multiple intersystem crossing and reverse intersystem crossing pathways, and high photoluminescence quantum yield. In addition, the TADF afterglow emitter of singlet excited state nature and millisecond lifetimes is conducive for efficient charge separation, which is the prerequisite for subsequent retard charge recombination and high-performance OLPL. Besides, the TADF emitter can simultaneously harvest singlet and triplet excitons upon retarded charge recombination to enhance OLPL. By employing a dopant-matrix strategy, SBF₂ molecules and N,N,N′,N′-tetramethylbenzidine (TMB, an electron donor that promotes charge separation) were doped into optimal crystalline organic matrix, phenyl 4-methoxybenzoate (MeOPhB), which protects excited states and acts as an electron acceptor. The resultant SBF₂-MeOPhB-TMB materials display bright OLPL with afterglow lasting up to 2 h. These materials hold significant potential for applications in anti-counterfeiting and data encryption. © 2025