Bridged <i>N</i> -Phenylphenazine-Based Multiresonance Emitters Enable Efficient Yellow Electroluminescence via Solution Process

Different from diphenylamine-based organoboron multiresonance (MR) emitters with blue-to-green emissions, this work presents the design and preparation of two boron and nitrogen-containing MR-TADF compounds (BDQuAc and BDSpQuAc) based on methylene and spirofluorene-bridged N-phenylphenazine ligands for efficient yellow narrowband organic light-emitting diodes (OLEDs). N-Phenylphenazine ligands with their strong electron-donating ability promote a short-range charge transfer (CT) effect within the MR skeleton, leading to red-shifted emission in toluene with peaks at 534–537 nm. The suppression of molecular rotation by the methylene and spirofluorene bridges results in a narrow emission spectrum, with a full width at half-maximum (fwhm) of only 0.16 eV. Concurrently, the enhanced molecular rigidity contributes to high photoluminescence quantum yields (PLQYs) of 90–95%. Meanwhile, compared to BDQuAc with a methylene bridge, BDSpQuAc based on a spirofluorene bridge exhibits weaker intermolecular aggregation with less dependence of photoluminescent spectra on doping level. The solution-processed OLED device incorporating BDSpQuAc demonstrates high-performance yellow emission with a peak at 559 nm, CIE coordinate values of (0.45, 0.54), and a maximum external quantum efficiency (EQEmax) of 17.9%, representing efficient yellow-emitting narrowband OLEDs by solution processing.