High-performance circularly polarized electroluminescence from d-f transition europium(II) complexes

Circularly polarized organic light-emitting diodes (CP-OLEDs) have attracted increasing interest for their advantages in generating circularly polarized light directly and efficiently. To date, chiral luminescent materials with different emission mechanisms have been investigated as emitters in CP-OLEDs, but it is difficult to achieve a high luminescence dissymmetry factor (g) and high efficiency simultaneously. Herein, chiral luminescent europium(II) complexes with d-f transition characteristics are synthesized and used as emitters in CP-OLEDs. The europium(II) complexes show a maximum g value of 6.6 × 10−3 in doped films, and the corresponding CP-OLEDs show a maximum external quantum efficiency up to 15.6%. The performance is attributed to the unique europium(II) complex with a d-f transition mechanism, which results in a theoretically high magnetic transition dipole moment and high exciton utilization efficiency. This study focusing on chiral d-f transition-containing lanthanide complexes opens up an avenue to future exploration of high-performance chiroptical materials.