Twins of Minimalistic Carbon Dots: Uniform Emitting‐Units and Molecular Level Repeatable Photoluminescence

Understanding the photoluminescence mechanism of carbon dots (C-dots) is both of fundamental and technical significance. However, it has remained an extreme challenge due to C-dots' indeterminate constitution and complicated composition/structure. Herein, a combined processing system, namely extraction and subsequent preparative thin layer chromatography for C-dots separation is presented. Benefiting from its powerful separation performances, two minimalistic C-dots with almost identical structure and optical properties (named as "twin" C-dots) are well separated. Then, by contrastive analysis, a photophysical picture for the C-dots' photoluminescence is presented: The C-dots' photoluminescence comes from uniform surface polycyclic aromatic hydrocarbon units instead of the whole particles, which is both size- and oxygen-independent. The products not only are highly bright and stable against photobleaching, but possess repeatable photoluminescence with molecular level accuracy. So, the C-dots favorably integrate the advantages from small molecule dyes to photoluminescent nanomaterials, which is unprecedented and desirable for property exploration and application expansion.