Red-shift emission and rapid up-conversion of B,N-containing electroluminescent materials via tuning intramolecular charge transfer

Abstract

Boron (B) and nitrogen (N)-based polycyclic aromatic hydrocarbons (PAHs) have been demonstrated as promising materials for building efficient thermally activated delayed fluorescent (TADF) emitters in blue and green regions, while red emission materials based on B,N systems are rare. Hence, to achieve a red-shifted emission peak over 600 nm by simply modifying the core of B,N-PAHs is a rewarding and challenging task. In this work, we demonstrate the para-D–π–B strategy implementation of modulating the predominance of locally excited (LE)/charger transfer (CT) states by introducing peripheral electron-donating units in a boron-carbazole containing backbone (BNCz) to develop four TADF emitters, BN-TC, BN-AC, BN-PXZ and BN-PZ. Due to the effect of different donor strengths on the excited states of these materials, we obtain full-color emission and a high photoluminescence quantum yield (Φ_PL) of nearly 100%. Notably, the device employing BN-PZ as a dopant exhibits orange-red emission with an electroluminescence (EL) peak at 612 nm. Meanwhile, this compound realizes very fast reverse intersystem crossing (RISC) with a rate constant (k_RISC) of 1.8 × 10⁶ s⁻¹, resulting in a device with a high external quantum efficiency (EQE) of 25.0% and low efficiency roll-off at high brightness.