Selenium-Containing Multi-Resonance Thermally Activated Delayed Fluorescence Host Material for Green and Red Phosphorescent OLEDs.

We report the molecular design and synthesis of a novel selenium-containing multi-resonance thermally activated delayed fluorescence (MR-TADF) host material, 3,6-di-tert-butyl-9,16-dioxa-15-selena-4b-boraindeno[2,1-a]naphtho[3,2,1-de]anthracene (TDBA-SePh), for green and red phosphorescent organic light-emitting diodes (PhOLEDs). By incorporating selenium into the DOBNA-based MR-TADF backbone, the reverse intersystem crossing (RISC) process was effectively activated, leading to enhanced utilization of triplet excitons. The corresponding RISC rate was determined to be 3.91 × 10 s. When applied to PhOLED devices, TDBA-SePh-based green and red OLEDs exhibited higher external quantum efficiency (EQE) and reduced efficiency roll-off compared to conventional mCP-based host materials. At a luminance of 1000 cd m, the green and red devices exhibited roll-off values of 2.5% and 4.3%, respectively. This improvement is attributed to the incorporation of selenium as a heteroatom, which accelerates the RISC process, thereby suppressing triplet-triplet annihilation (TTA). These results suggest that adopting a similar molecular design strategy can not only reduce efficiency roll-off but also enhance device efficiency and operational stability, offering significant potential for future OLED applications.