Oxygen-Doped Carbon Rings for Pure Violet Light-Emitting Diodes
High-colour-purity light-emitting diodes (LEDs) are essential for next-generation wide-colour-gamut displays and emerging photonic technologies. While narrow-band blue emitters with high photoluminescence quantum yield (PLQY) have been developed via para-positioned boron and nitrogen doping, extending emission to pure violet (<400 nm) remains challenging. Here, we highlight a breakthrough by Song and coworkers (Nature Synthesis, 2024) who synthesized oxygen-doped carbon quantum rings (OD-CQRs) via a one-step solid-state reaction between 2,3-dihydroxynaphthalene and anhydrous SnCl2 at 180 °C. High-resolution STM at 4.7 K revealed a planar hexagonal ring structure (diameter 18.8 Å) with alternating benzene and oxygen-containing five-membered heterocycles. The OD-CQRs exhibit pure-violet emission centered at 393 nm with an ultranarrow full-width at half-maximum (FWHM) of 18 nm and an exceptional PLQY of 95%—the best combination among carbon-based luminescent materials. The innovative O-π confinement strategy restricts π-electron delocalization and suppresses non-radiative vibrational relaxation, as confirmed by DFT, localized orbital locator (LOL), and nucleus independent chemical shifts (NICS) analyses. The root mean square displacement between ground and excited states is only 0.0 Å, indicating minimal structural reorganization. This work provides a simple, scalable route to high-performance violet emitters, addressing a critical bottleneck in display and photonic technologies.