Ultra-high-definition OLED displays demand emitters with extremely high color purity to satisfy the stringent BT.2020 color gamut standard. Among the three primary colors, the development of narrowband pure-red emitters remains one of the greatest challenges because extending emission into the red region generally leads to stronger vibronic coupling, increased nonradiative decay, and severe spectral broadening. As a result, 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, the research team led by Prof. LU Canzhong and Prof. CHEN Xulin from the Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences reported a modular molecular design strategy that enables ultra-narrowband pure-red multi-resonance emitters approaching the BT.2020 color standard through chlorine-oriented double borylation and peripheral acceptor extension.

The 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.

Furthermore, strong intramolecular hydrogen bonds between the triazine units and the 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 enabled substantial red-shifted emission while preserving the intrinsic narrowband characteristics of the MR framework.

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 standard.

To efficiently harvest electrically generated triplet excitons, the team further incorporated BNNAP-tBuTRZ as the terminal emitter into phosphor-assisted TADF-sensitized fluorescence OLEDs. The resulting device delivered 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 requirement. It achieved a maximum EQE 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, collectively ranking among the best reported performances for pure-red OLEDs.

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.

(a) Diagram explanation for the importance of spectral narrowing for red emitters, and (b) and (c) molecular design strategies for the MR-type red emitters. (Image by Prof. CHEN)

Contact

Prof. CHEN Xulin
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Sciences
Email: xlchen@fjirsm.ac.cn