Temperature-gradient method for gaining insights into the luminescence origin and formation mechanism of carbon dots

Carbon dots (CDs) are a fascinating new class of fluorescent nanomaterials, yet the understanding of the fluorescent origin of CDs still lags well behind their applications. The key challenges for unveiling the fluorescent mechanism of CDs relate to the insufficient basis for structural evaluation. This work presents a temperature-gradient route to control the bottom-up approach of CDs, enabling the precise structural characterization of intermediates and the establishment of definite structure-property relationships, akin to the domino reaction synthesis of complex natural products from small organic molecules. Taking the binary components citric acid and meta-dimethylaminophenol generated CDs as a case study, their emissive mechanism, particularly the unique excitation-dependent fluorescence behavior, is reasonably explained and supported by structural evaluation through retrosynthetic analysis. The formation process of CDs is investigated using a combination of spectroscopic, thermal, and theoretical calculation techniques, demonstrating the significant potential of the temperature-gradient route in the exploration structure-property relationships and guiding the rational design of advanced CD applications.