Advanced charge transfer technology for highly efficient and long-lived TADF-type organic afterglow with near-infrared light-excitable property

Heavy atom effects and n-π* transitions have been frequently reported to enhance room-temperature organic phosphorescence efficiency but lead to shortage of phosphorescence lifetimes. Unlike these reported studies, we conceive the incorporation of advanced charge transfer (CT) technology to boost room-temperature organic afterglow efficiency and simultaneously maintain afterglow lifetimes. Here we design difluoroboron β-diketonate (BF 2 bdk) CT compounds with moderate singlet-triplet splitting energy (Δ E ST ) of around 0.4 eV, and relatively large spin-orbit coupling matrix elements (SOCME(S 1 -T 1 ), 1–10 cm −1 ) to achieve efficient intersystem crossing (ISC) and moderate rates of reverse intersystem crossing ( k RISC , 1–10 s −1 ). The advanced CT technology, which includes multiple electron-donating groups and orthogonal donor-acceptor arrangement, have been found to narrow Δ E ST and enhance both ISC and RISC. Meanwhile, the organic matrices suppress nonradiative decay of BF 2 bdk’s T 1 states by their rigid microenvironment. Consequently, thermally activated delayed fluorescence (TADF)-type organic afterglow materials can be achieved with afterglow efficiency up to 83.0%, long lifetimes of 433 ms, excellent processablility, as well as advanced anti-counterfeiting and information encryption. Furthermore, with the aid of up-conversion materials and through radiative energy transfer, TADF-type afterglow materials with aqueous dispersity and near-infrared light- excitable property have been achieved, which paves the way for biomedical applications.