ThermallyActivated Delayed Fluorescence-Type OrganicAfterglow Emitters for Devising Organic Long Persistent LuminescenceMaterials

Organic long persistent luminescence (OLPL) materials exhibit afterglow lasting several hours. However, current strategies for constructing OLPL materials remain limited, necessitating further exploration. Herein, a difluoroboron β-diketonate (BF₂bdk) luminophore was designed, featuring high molar absorptivity, abundant intersystem crossing and reverse intersystem crossing (RISC) pathways, and an enhanced photoluminescence quantum yield (PLQY). The BF₂bdk was doped into an optimal crystalline matrix, 4-methoxyphenyl benzoate (MeOPhB), which serves to protect excitons while also acting as electron acceptors. The resulting BF₂bdk-MeOPhB materials possess moderate <i>k</i>_RISC, exhibiting bright thermally activated delayed fluorescence (TADF) afterglow with 1.5 s duration and 73.1% PLQY. Under intense excitation, this two-component system demonstrated two-photon-ionization-triggered OLPL. Furthermore, the addition of a third component, <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylbenzidine (TMB), acts as an electron donor, promoting charge separation. Following the slow charge recombination, high-performance BF₂bdk-MeOPhB-TMB OLPL materials based on TADF-type afterglow emitters were achieved with 2 h afterglow duration, showing promising applications in anticounterfeiting and data encryption.