Highly Efficient Narrow‐Emitting Circularly Polarized Organic Light‐Emitting Diode with an Intramolecular Sensitization Mechanism by Through‐Space Energy Transfer

Solution-processable circularly polarized (CP) organic light-emitting diodes (OLEDs) are unique devices generating CP electroluminescence. However, the efficiency of solution-processed CP OLEDs is still low compared with vacuum-processed CP OLEDs. In this work, highly efficient and narrow-emitting solution-processed CP OLEDs are developed using a novel multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitter operated by an intramolecular TADF sensitized MR-TADF emission mechanism. The CP-type MR-TADF emitter is designed to have a TADF antenna unit and a terminal MR-TADF unit connected through a planar chiral unit. The TADF antenna unit plays the role of initial exciton generator, harvesting both singlet and triplet excitons, and the exciton energy is transferred to the terminal MR-TADF unitby through-space energy transfer. As a result, the external quantum efficiency (EQE) of the chiral MR-TADF emitter is significantly enhanced from 16.2% of the MR-TADF emitter without the TADF antenna unit to 28.0% by solution process. The CP OLEDs showed an electroluminescence dissymmetry factor of 10^-3 order, demonstrating that the molecular design is also effective to achieve highly efficient CP emission in OLED. This work establishes an effective strategy for realizing highly efficient narrowband CP electroluminescence via intramolecular TADF-sensitized MR emission.