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

In organic systems, it is very challenging to simultaneously achieve long afterglow lifetimes (tau(AG)) and high afterglow efficiency (phi(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 phi(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 phi(AG) to 64%, and maintain long tau(AG) > 1.0 s. The obtained materials display intense afterglow brightness, excellent processability, and temperature-sensing function.

Automated summary

By designing luminescent dopants with specific characteristics, controlling molecular rigidity, screening organic matrices, and deuterating luminescent dopants, it is possible to achieve long afterglow lifetimes and high afterglow efficiency in organic materials.