A Multiple Resonance Emitter Integrating Para‐B‐π‐B′/Meta‐N‐π‐N Pattern via an Unembedded Organoboron Decoration for Both High‐Efficiency Solution‐ and Vacuum‐Processed OLEDs

Abstract Multiple resonance (MR)‐type thermally activated delayed fluorescence (TADF) emitters have promising prospects for high‐color‐purity organic light‐emitting diodes (OLEDs), but they are seldom attempted in the fabrication of solution‐processed devices. In addition, another issue with MR‐TADF emitters is that their heteroatom patterns are very limited, hampering their diversity. Herein, a novel double boron (B)‐containing MR‐TADF paradigm that merges an unembedded organoboron unit and a B‐embedded π‐fused MR framework into one system, furnishing a unique para ‐B‐π‐B′/ meta ‐N (nitrogen)‐π‐N molecular pattern is proposed. Based on this, a proof‐of‐concept molecule, BNB ′ ‐1 , is developed, simultaneously achieving a bright sharp emission peaking at 540 nm with a full width at half maximum (FWHM) of only 24.5 nm/98 meV, a nearly unity photoluminescence quantum yield and excellent organic solubility. A solution‐processed OLED using BNB′‐1 emitter delivers an impressive external quantum efficiency (EQE) as high as 36.2% with an emissive FWHM of only 30.0 nm/0.13 eV at ≈540 nm; both parameters set new records among the ever‐reported solution‐processed MR‐OLEDs. Moreover, BNB′‐1 also obtains a superhigh EQE of 40.3% in vacuum‐processed OLEDs, surpassing all MR‐OLEDs in the similar emission region. This work provides an interesting solution to develop high‐performance solution‐processable MR‐TADF emitters with diverse heteroatom patterns.