Toward Ultra‐Narrowband Long‐Wavelength Multiple‐Resonance Emitters: Mechanistic Insights and Design Principles

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) material represents a groundbreaking advancement in organic electronics, enabling ultra-narrowband emission with the enhanced efficiency and spectral accuracy. Leveraging the MR effect, MR-TADF materials inherently achieve narrow emission profiles that are crucial for High-definition display. These materials offer a significant advantage over traditional phosphorescence and TADF emitters, which enable high-performance organic light-emitting diodes (OLEDs) with intrinsically narrow emission spectra. However, realizing full-color ultra-narrowband emission is hindered by the intrinsic conflict between spectral tunability and narrowing of the emission bandwidth. Overcoming these challenges requires a deep understanding of the spectral narrowing mechanisms and the integration of precise molecular design strategies that balance efficiency, tunability, and emission purity. This review provides an overview of the principles behind spectral narrowing in boron/nitrogen-doped MR emitters, including the fundamental mechanisms, quantitative metrics, and recent breakthroughs. It also discusses the challenges and future prospects for achieving ultra-narrowband emission across the full visible spectrum, offering strategic guidance for the future development of OLED materials with enhanced color purity and performance.