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.