Boosting organic afterglow efficiency via triplet–triplet annihilation and thermally-activated delayed fluorescence

Abstract

Due to the spin-forbidden nature of organic phosphorescence, it is challenging to achieve high afterglow efficiency in room-temperature organic afterglow systems, especially for those with long afterglow emission wavelengths. Here we report the incorporation of triplet–triplet annihilation (TTA) and thermally-activated delayed fluorescence (TADF) mechanisms to significantly enhance the organic afterglow efficiency in dopant–matrix systems under ambient conditions. Difluoroboron β-diketonate (BF₂bdk) compounds are selected as luminescent dopants and designed with naphthalene functional groups to show a relatively strong tendency of intersystem crossing. 4-Methoxybenzophenone matrices are employed to facilitate intersystem crossing of BF₂bdk excited states via dipole–dipole interactions and meanwhile suppress nonradiative decay and quenching of BF₂bdk triplet excited states. Besides phosphorescence decay, the dopant–matrix systems exhibit additional pathways to harvest triplet energies via TTA and TADF, leading to the significant improvement of the organic afterglow efficiency. The afterglow materials can be melt-cast into desired shapes, can function as multicolor-encoded anti-counterfeiting objects, and can be processed into aqueous dispersions, which display background-free bioimaging properties.