High‐Efficiency and Narrow‐Band Near‐Ultraviolet Emitters with Low CIE _y of 0.03 by Incorporating Extra Weak Charge Transfer Channel into Multi‐Resonance Skeleton

Abstract

Hybridized local and charge‐transfer (HLCT) excited‐state emitters can effectively utilize non‐radiative triplet excitons through high‐lying reverse intersystem crossing (hRISC), but they are mostly limited to the donor‐ π‐acceptor type molecules. It is a great challenge to develop high‐performance near‐ultraviolet (NUV) emitters with narrow‐band emission by HLCT due to the large carrier injection barriers and high triplet energy. In this work, by incorporating planar multi‐resonance (MR) skeleton of oxygen‐bridged triphenylborane (BO) and weak electron‐donating unit of tetraphenyl‐silane (TPS), two NUV emitters of tBOSi and tBOSiCz are developed, where an extra weak charge transfer (CT) channel between BO skeleton and peripheral phenyl in TPS is observed to increase CT component and activate hot exciton channel of hRISC. As a result, tBOSi and tBOSiCz show an outstanding narrow‐band NUV emission at 414 nm with a FWHM of about 32 nm in solution‐processed organic light‐emitting diodes (OLEDs), even at a heavy doping ratio. The best NUV electroluminescent properties are further achieved in the optimal tBOSi‐doped OLEDs with a record efficiency of 9.15% and a low CIE _y of 0.034. This work provides a profound guidance for developing high‐performance narrow‐band NUV emitters by an extra weak CT channel into MR skeleton to activate HLCT emission.