Polyphenylene molecular engineering enables highly efficient multi-resonance thermally activated delayed fluorescence emitters with quenching resistance

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials have emerged as promising candidates for organic light-emitting diodes (OLEDs) due to their narrow emission spectra and exceptionally high photoluminescence quantum yields (PLQYs). Nevertheless, the rigid planar molecular architecture of MR-TADF materials inherently induces severe aggregation-caused quenching (ACQ) originating from π-π stacking interactions between MR chromophores, which consequently causes significant deterioration of device performance. Herein, we developed two novel emitters, namely BN-TB and BN-PB, through strategic incorporation of three-dimensionally steric-hindered tetraphenylbenzene (4Ph) units into the peripheral architecture of MR frameworks. The strategic integration of 4Ph moieties induces long-range charge transfer (LRCT) characteristics, achieving high the reverse intersystem crossing rate (k_RISC) for BN-TB (4.52 × 10⁴ ∼ 4.27 × 10⁴ s⁻¹) and BN-PB (6.36 × 10⁴ ∼ 5.51 × 10⁴ s⁻¹) as the doping concentration increased from 5 to 30 wt%. This significantly enhances the solid-state anti-quenching capability, with the PLQY decreasing modestly from 91 % to 81 % for BN-TB and from 96 % to 88 % for BN-PB. Additionally, the introduction of 4Ph groups improves the electron transport performance of the molecule, resulting in more balanced carrier transport in OLEDs. Therefore, OLEDs based on two emitters achieved high maximum external quantum efficiencies (EQE_maxs) of 35.9 % for BN-TB and 37.1 % for BN-PB, respectively. More importantly, the devices maintained impressive EQEs of 27.3 % and 31.1 %, even at doping ratio of 30 wt%. This work establishes a novel molecular design approach for developing high-efficiency MR-TADF materials with excellent anti-quenching characteristics and balanced carrier transport performance.