Tetrahedral Structure Based on Triphenylgermanium for Quenching‐Resistant Multi‐Resonance Thermally Activated Delayed Fluorescence Emitters

Abstract The rigid planar architecture of multiple resonance thermally activated delayed fluorescence (MR‐TADF) molecules employing boron/nitrogen (B/N) frameworks typically results in severe aggregation‐caused quenching (ACQ) and spectral broadening. Herein, a steric modification strategy is proposed by incorporating a tetrahedral architecture of triphenylgermanium (TPhGe) into the para‐position of B/N/N, B/N/O, and B/N/S frameworks for the first time, formed three MR‐TADF emitters, BNNGe, BNOGe, and BNSGe, with narrowband emissions ranging from bluish‐green to pure blue. Consequently, these emitters exhibit high photoluminescence quantum yields of > 90% in doped films. Organic light‐emitting diodes (OLEDs) based on BNNGe, BNOGe, and BNSGe demonstrate impressive maximum external quantum efficiencies (EQE_maxs) of 30.1% to 15.5%, and 20.7%, respectively. The unique tetrahedral TPhGe moiety, with its bulky size conformation, effectively separates adjacent MR‐TADF molecules, resulting in efficient luminescence across a broad range of doping concentrations (5–30 wt%) in doped films, thereby successfully suppressing the ACQ in devices. Furthermore, OLEDs containing BNSGe display low‐efficiency roll‐offs because of higher spin‐orbital coupling and reverse intersystem crossing rates of the emitter, attributed to the heavy atom effect. Notably, the device with 5 wt% BNOGe exhibits a pure blue emission peaking at 461 nm, with a narrow full‐width at half‐maximum of 32 nm.