Exciton lifetime is a critical factor in determining the performance of optoelectronic functional systems and devices. Thermally activated delayed fluorescence (TADF) emitters that can concurrently achieve a high fluorescence quantum yield and short exciton lifetime are desirable for application in organic light-emitting diodes (OLEDs) with suppressed efficiency roll-off. Herein, phenoxaborin and xanthone-cored TADF emitters with quadrupolar electronic structures are reported to exhibit sub-microsecond TADF lifetimes as short as 650 and 970 ns, respectively, while preserving high fluorescence quantum yields. By extending the El-Sayed rule to the quadrupolar π-systems, the contribution of doubly degenerate charge-transfer excited states induced by dual donor units can enhance the spin–orbit coupling between them, leading to a spin-flip acceleration between the excited triplet and singlet states. This electronic feature is advantageous for mitigating exciton annihilation processes in the emission layer, thereby reducing the efficiency roll-offs in OLEDs. Consequently, a high external electroluminescence quantum efficiency over 20% can be retained, even under operating the device at a high luminance of 1000 cd m−2.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics