Spiral‐Locking Strategy for Efficient Narrowband Multiple Resonance Thermally Activated Delayed Fluorescence Emitters

Multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials are applied in organic light‐emitting diodes (OLEDs) due to their high efficiency and color purity. However, the inherent planar structure of MR emitters presents significant challenges, including concentration‐induced emission quenching, spectral redshift and broadening. To address these issues, two orthorhombic asymmetric conformational materials, SBNO and SBNOS, have been developed. Both MR‐TADF emitters incorporate a sterically hindered spiro‐carbon bridge to minimize intermolecular chromophore interactions. Consequently, the spectra of the SBNOS‐based devices exhibit only a 4 nm redshift and a 7 nm broadening of the full‐width at half maximum (FWHM) across a doping ratio range of 1–100 wt%. The steric effect produces pure green OLEDs with a CIE y of 0.69 and enhances performance, achieving a maximum external quantum efficiency (EQEmax) of up to 32.7%. The referent BNO without spiro skeleton suffers from serious spectral redshift and broadening as well as a lower device efficiency. This research demonstrates a promising approach to developing MR‐TADF devices that resist redshift and broadening while maintaining high color purity and efficiency. A spiro‐locked strategy is introduced to develop MR‐TADF emitters in rigid orthogonal configurations. The SBNOS‐based OLED achieves a high external quantum efficiency of 32.7%, along with narrowband emission and minimal redshift.