Spin-Enhanced Reverse Intersystem Crossing and Electroluminescence in Copper Acetate-Doped Thermally Activated Delayed Fluorescence Material.

Thermally activated delayed fluorescence (TADF) materials are attractive for next-generation organic light-emitting diodes (OLEDs) because of their utilization of nonradiative triplets via reverse intersystem crossing (RISC), which requires not only a small singlet-triplet energy splitting but also the conservation of spin angular momentum. Here we use copper acetate as a spin sensitizer to facilitate RISC and thus enhance electroluminescence in TADF-exciplex OLEDs. Copper acetate is involved in the radiative decay process due to its coordination interaction with exciplex molecules having intermolecular charge-transfer characteristics, which causes significant changes in the photoluminescence intensity and lifetime. Meanwhile, magneto-photoluminescence reveals that the addition of copper acetate promotes spin conversion in the RISC process. It allows the enhancement of the electroluminescence (∼80%) from spin-sensitized OLEDs, accompanied by the suppression of magneto-electroluminescence upon the doping of copper acetate. These results illustrate that using a spin sensitizer may overcome the limitation of harvesting nonradiative triplets in organic luminescent materials and devices.