Manipulation of Triplet Excited States for Long‐Lived and Efficient Organic Afterglow

Abstract In organic systems, it is very challenging to simultaneously achieve long afterglow lifetimes (τ _AG ) and high afterglow efficiency (Φ _AG ). Here, luminescent dopants which feature a small rate of phosphorescence decay ( k _P ) and modest rate of reverse intersystem crossing ( k _RISC ) are designed and k _nr + k _q values (nonradiative decay and quenching) of triplet excited states are suppressed by all means that include increasing molecular rigidity of luminescent dopants, screening organic matrices to strongly inhibit intramolecular motions of luminescent dopants, and deuteration of the luminescent dopants. Organic matrices are selected with large dipole moments to stabilize the singlet excited states of luminescent dopants via dipole–dipole interactions, reduce singlet–triplet splitting energy, and thus enhance Φ _ISC , leading to significant population of triplet excited states. Thermally activated delayed fluorescence mechanism is also used with modest k _RISC to harvest triplet energies, significantly improve Φ _AG to 64%, and maintain long τ _AG > 1.0 s. The obtained materials display intense afterglow brightness, excellent processability, and temperature‐sensing function.