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.