Ultra-high-definition organic light-emitting diode (OLED) displays demand emitters with extremely high color purity to satisfy the BT.2020 color gamut standard. Among the three primary colors, the development of narrowband pure-red emitters remains a challenge. Organic emitters simultaneously featuring an emission full width at half maximum (FWHM) below 0.1 eV and a CIE-x value above 0.67 (NTSC red standard) are exceedingly rare.

In a study published in Advanced Functional Materials, a research team led by Prof. LU Canzhong and Prof. CHEN Xulin from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences developed a modular molecular design strategy which enables ultra-narrowband pure-red multi-resonance emitters approaching the BT.2020 color gamut standard.

Researchers constructed a synthetically accessible para-boron-substituted naphthalene multi-resonance (MR) platform using a chlorine-oriented double borylation strategy, and introduced peripheral triazine acceptors in a nearly coplanar configuration, enabling effective modulation of the emission wavelength toward the pure-red region.

Strong intramolecular hydrogen bonds between triazine units and MR core effectively locked the molecular conformation, minimizing long-range twisted intramolecular charge transfer and reducing high-frequency vibrational modes responsible for spectral broadening. This molecular design strategy enables substantial red-shifted emission while preserving intrinsic narrowband characteristics of the MR platform.

The resulting emitters, BNNAP-tBuTRZ and BNNAP-PhTRZ, exhibited near-unity photoluminescence quantum yields (98.7% and 98.1%) with pure-red emission peaks at 625 and 633 nm and exceptionally narrow FWHMs of only 24.6 and 25.3 nm (0.078 eV), respectively. Their CIE coordinates reached (0.69, 0.31) and (0.70, 0.30), approaching the BT.2020 red color gamut standard.

To efficiently harvest electrically generated triplet excitons, researchers incorporated BNNAP-tBuTRZ as the terminal emitter into phosphor-assisted thermally activated delayed fluorescence (TADF)-sensitized fluorescence OLEDs.

The resulting device delivered one of the best performances for pure-red OLEDs. Its ultranarrow pure-red emission centered at 629 nm with an exceptionally narrow FWHM of 31.9 nm (0.10 eV) and CIE coordinates of (0.69, 0.31), approaching the BT.2020 red color gamut standard. It achieved a maximum external quantum efficiency of 26.6%, a power efficiency of 33.8 lm W^-1, a maximum luminance of 56,900 cd m^-2, and an extrapolated LT80 lifetime exceeding 19,000 h at an initial luminance of 100 cd m^-2.

This work presents an efficient design strategy for red emitters that simultaneously achieves high color purity, ultra-narrowband emission, high efficiency, and synthetic simplicity, offering promising material candidates for next-generation wide-color-gamut OLED displays.