Construction of Near‐Infrared Organic Long‐Afterglow Materials via Efficient Cascaded Förster Resonance Energy Transfer

energy level promote nonradiative decay. Constructing efficient organic room temperature phosphorescence (RTP) materials that emit near-infrared afterglow remains challenging. Thus, we doped (9-phenyl-carbazol-2-yl)-boric acid into the polyvinyl alcohol to obtain a phosphorescence film with excellent photophysical performance. Then this film was used as the donor for resonance energy transfer and the near-infrared dye Nile Blue was selected as the energy acceptor. To address the lack of spectral overlap between the donor emission and the acceptor absorption, fluorescein and rhodamine B were introduced as mediators, thereby constructing a four-component co-doped cascade resonance energy transfer system. Through highly efficient cascade triplet-singlet and singlet-singlet Förster resonance energy transfer, this film achieved a near-infrared ultra-long afterglow emission at 695 nm and a lifetime of 562 ms. Remarkably, the total cascade energy transfer efficiency reached 66.01% and the total photoluminescence quantum yield was 28.72%. Furthermore, based on the multicolor and time-dependent performance of this luminescent material, a six-layer anti-counterfeiting and encryption system was designed. Finally, the extended experimental results demonstrated the promising prospects for achieving near-infrared luminescence in cascaded systems.