Efficient Ultra‐Narrowband Green Emitters Achieved by Integrating a C═O/N‐Type Multi‐Resonance Skeleton With Bis‐Spiro Structures

Narrowing the emission bandwidth of thermally‐activated delayed fluorescence (TADF) systems has become a strategic priority for the development of wide‐color‐gamut and low‐power‐consumption organic light‐emitting diode (OLED) displays. Although TADF systems with C═O/N‐embedded multi‐resonance (MR) skeletons have shown great potential for narrowband emission, those achieving efficient electroluminescence with a full‐width at half‐maximum (FWHM) below 20 nm remain elusive. Here, we disclose that through integrating a C═O/N‐type MR‐skeleton with bis‐spiro structures, planarization of the MR skeleton is achieved by balancing repulsion between the MR‐skeleton and surrounding steric protecting groups. Meanwhile, molecular vibrations are suppressed so that the main emission band is narrowed and the shoulder intensity is reduced. The two designed emitters achieve an FWHM of merely 13 nm in toluene. Moreover, an OLED device of one emitter achieves an FWHM of 19 nm along with excellent Commission Internationale de l'Éclairage coordinate of (0.17, 0.72) and a maximum external quantum efficiency exceeding 30%. This study provides theoretical and experimental insights for designing C═O/N‐type MR‐TADF systems with ultra‐narrowband emission, facilitating their development for display applications.