Dual-Mechanism Design\nStrategy for High-Efficiency\nand Long-Lived Organic Afterglow Materials

Organic room-temperature phosphorescence (RTP) and afterglow\nmaterials\nhold great potential for various applications, but there remain inherent\ntrade-offs between the afterglow efficiency and the lifetime. Here,\nwe propose a dual-mechanism design strategy, leveraging the RTP or\nthermally activated delayed fluorescence (TADF) mechanism for a high\nafterglow efficiency and the organic long-persistent luminescence\n(OLPL) mechanism for a prolonged afterglow duration. The intramolecular\ncharge transfer (ICT)-type difluoroboron β-diketonate molecules\nwith a large S<sub>1</sub> dipole moment are doped as the luminescent\ncomponent into the organic matrix with a large dipole moment, and\na series of TADF-type afterglow materials can be achieved with an\nafterglow efficiency of up to 88.7% and an afterglow lifetime of 200\nms. To prolong the afterglow duration, an electron donor is introduced\nas the third component to generate traps and facilitate charge separation.\nThe obtained materials exhibit a dual afterglow mechanism, first exhibiting\na TADF/RTP afterglow with an afterglow efficiency of up to 50.9%,\nfollowed by an hours-long OLPL afterglow emission with an afterglow\nefficiency of up to 13.1%. Further investigations reveal that an appropriate\nheavy-atom effect can facilitate the intersystem crossing process,\nwhich can promote the charge separation process and thus improve the\nOLPL afterglow performance. Additionally, rare-earth upconversion\nmaterials are introduced into OLPL materials to enable their near-infrared\nexcitation properties, showcasing their potential applications in\nbioimaging.