With the growing demand for ultra-high-definition (UHD) flexible display devices, research on narrowband organic emitters and related organic light-emitting diode (OLED) devices that meet the BT.2020 emission standard has attracted considerable attention. However, as narrowband emitters for blue and green have become relatively mature in research and application, the counterpart (red emitters) with both high efficiency and practical application prospects remains a key challenge in this field.
Polycyclic aromatic hydrocarbons (PAHs) and their derivatives are important organic molecules widely used in organic functional materials, including OLEDs, organic thin-film transistors (OFETs), and organic solar cells (OPVs). Both theoretical and experimental results demonstrate that the fused topological structures of PAH molecules directly determine their π-electron distribution, aromaticity, and excited-state dynamic behavior. Based on these findings, You and Bin et al. from Sichuan University proposed π-electron delocalization of classic PAHs through skeleton reconstruction. This strategy enables the controllable transition of aromaticity from global delocalization to local localization, restricts long-range π-electron delocalization, suppresses excited-state vibrational coupling, and thus promises intrinsically narrow-spectrum emission materials.
As a proof of concept, the authors systematically reconstructed pyrene, coronene, and ovalene into a series of PAHs with diverse structures. Calculations of nucleus-independent chemical shift (NICS) and excited-state energies reveal that fused topological structures can significantly modulate molecular aromaticity and emission wavelength. Subsequently, the authors selected M15 as an ideal molecular skeleton for the synthesis of derivatives. Photophysical studies show that emitter 2 based on the M15 skeleton exhibits a sharp fluorescence emission peaked at 620 nm with a full width at half maximum (FWHM) of only 20 nm. To achieve fine-tuning of the red emission, the authors synthesized a series of derivatives based on 2 . These derivatives emit at wavelengths ranging from 618 to 630 nm, maintain FWHM values below 25 nm, and achieve fluorescence quantum yields of up to 80%. Through systematic comparison, molecules 2 and 7 were finally chosen as emitters for the fabrication and performance investigation of OLED devices.
Based on the phosphorescence-sensitized fluorescence (PSF-OLED) strategy, the authors employed these two molecules as emitters in OLED devices. According to the optimized device measurements, the device based on molecule 2 achieved a maximum external quantum efficiency (EQE) of 20.2%, with an electroluminescence peak at 634 nm, an FWHM of 26 nm, and CIE coordinates of (0.698, 0.298). Encouragingly, molecule 7 exhibited a red-shifted emission peak at 639 nm. Although its FWHM slightly increased to 28 nm, the CIE coordinates (0.704, 0.294) closely matched the BT.2020 red standard. Meanwhile, the EQE was significantly improved to a record-high 24.2%. This performance represents the highest efficiency for traditional fluorescent-molecule-based OLEDs complying with the BT.2020 red standard, and also the narrowest FWHM among all reported BT.2020-compliant red OLEDs.
National Science Review
Experimental study