Topological Carbon Quantum Rings With Near-Unity Photoluminescence for Efficient Sky-Blue Electroluminescence

Carbon quantum dots (CQDs) are promising environmentally benign emitters for next-generation optoelectronic devices, yet aggregation-caused quenching (ACQ) fundamentally limits their solid-state emission efficiency. Existing strategies primarily rely on surface or morphological modifications, while the role of topology in regulating exciton behavior remains largely unexplored. Here, we report a topological design strategy to suppress ACQ by constructing carbon quantum rings with a closed-loop conjugated architecture. Guided by symmetric molecular precursors, the ring formation process is elucidated by combined mass spectrometry and density functional theory (DFT) calculations, revealing a thermodynamically driven evolution from planar oligomers to curved and ultimately closed-loop structures. This unique topology intrinsically suppresses intermolecular π-π coupling and non-radiative decay, while enabling exciton confinement within a rigid conjugated framework. As a result, the carbon quantum rings exhibit a near-unity photoluminescence quantum yield of 99.5% in solution and 58.9% in solid-state films. When integrated into electroluminescent devices, efficient sky-blue emission is achieved with a low turn-on voltage of 2.8 V, a maximum luminance of 1020 cd m^-2, and an external quantum efficiency of 3.4%. This work establishes topology as a fundamental design parameter for carbon-based emitters and provides a general strategy for overcoming ACQ in sustainable optoelectronic materials.