Molecular Design and Synthesis of Narrowband Near-Ultraviolet and Pure Deep-Blue Thermally Activated Delayed Fluorescence Materials by an Ether Group Strategy

Boron-containing polycyclic aromatic hydrocarbons are promising materials for the development of displays due to their multiple-resonance thermally activated delayed fluorescence (MR-TADF) with narrowband emission. However, except for electrophilic aromatic borylation reactions, synthetic strategies for the generation of boron-containing MR-TADF molecules remain virtually unexplored. In particular, the synthesis of MR-TADF emitters that exhibit narrow near-ultraviolet and pure deep-blue emission constitutes a challenging task. Here, we present a directed tri-ortho-lithiation–borylation approach that provides a new family of N,N-bridge-type triphenylboranes that bear phenylimino groups instead of the methylene groups at the 8- and 14-positions and ether groups instead of the hydrogen atoms at the 3- and 19-positions of 1-borapentacyclohenicosanonaene. The effects of the electron-donating resonance of the oxygen atoms of the ether groups and the incorporation of oxygen atoms in the six-membered cycle allow the precise tuning of the HOMO–LUMO energy gaps, resulting in narrowband near-ultraviolet and pure deep-blue TADF with Commission-International-de-l’Éclairage coordinates (CIE_x,y) of (0.142–0.160, 0.029–0.063) for the photoluminescence (PL) and (0.146–0.160, 0.026–0.053) for the electroluminescence (EL). The CIE_x,y for the EL meet the BT.2020 requirement for the blue primary of ultrahigh-definition displays.