Thermally activated delayed fluorescence emitters with bulky four-coordinate boron acceptors for high-performance solution-processed OLEDs

Although considerable progress has been made in vacuum-deposited thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs), the development of inexpensive solution-processed TADF-OLEDs still lags, primarily owing to low luminous efficiency. Herein, we designed and synthesized two TADF emitters by introducing bulky four-coordinate boron into pyrimidine acceptor, producing a simple and versatile approach to dramatically enhance performance. The introduction of bulky four-coordinate boron substantially reduces the singlet-triplet energy gap and improves photoluminescent quantum yield as well as improves solubility by inhibiting intermolecular aggregation or crystallization, resulting in an excellent TADF characteristics and highly efficient solution-processed OLEDs. Finally, the Spiro-PMB-SPAc emitter provides an OLED device with a remarkable maximum external quantum efficiency of 38.21 %, which reaches 32.50 % at a luminance of 500 cd m- 2. This state-of-the-art performance validates the superiority of the boron-nitrogen coordination strategy in the reconstruction of pyrimidine-based TADF molecules for highly efficient solution-processed OLEDs.