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

ABSTRACT

Near‐infrared organic materials with long afterglow at room temperature hold tremendous potential for applications in fields such as bioimaging and anti‐counterfeiting. However, their low T ₁ 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.