Peripheral Substitution Engineering of MR-TADF Emitters Embedded With B‒N Covalent Bond Towards Efficient BT.2020 Blue Electroluminescence.

Abstract

Compared with the classical boron/nitrogen (B/N) doped ones, multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters embedded with B-N covalent bond behave a significantly blue-shifted narrowband TADF, and thus show a greater potential in ultrapure blue organic light-emitting diodes (OLEDs). As a proof of concept, herein a peripheral substitution engineering is demonstrated based on such a B‒N embedded parent core. The simple approach is found to ensure easy synthesis via a one-pot lithium-free borylation-annulation, manipulate the excited states through different electronic coupling between core and substituent, and introduce the steric hindrance to minimize the unwanted spectral broadening. Impressively, ultrapure blue OLEDs are realized to give a high external quantum efficiency of 20.3% together with Commission Internationale de l'Éclairage coordinates of (0.152, 0.046). The performance is well competent with those of B/N doped MR-TADF emitters, clearly highlighting that the B‒N embedded framework is a novel promising paradigm towards efficient BT.2020 blue standard.