Extraction of Dual‐Switch Fluorescent Nanosheets from Asphaltenes under Ambient Conditions

Abstract Asphaltene, often regarded as an undesirable by‐product of petroleum processing, possesses abundant reserves but limited market value. In this study, a simple and environmentally friendly solvent extraction method is conducted under ambient conditions to convert low‐value asphaltene into high‐value asphaltene‐based fluorescent carbon nanosheets (a‐FCS). This approach yields dual‐switch a‐FCS capable of emitting orange‐red fluorescence in solid‐state or water environment and exhibiting blue‐to‐yellow fluorescence in organic solvents. Moreover, the redshift observed in the fluorescence emission wavelength in the solvent is attributed to its intrinsic self‐assembly behavior, which becomes more pronounced with increasing concentration. Upon introduction to water, hydrophobic interactions induce the aggregation of a‐FCS. This aggregation triggers the orange‐red fluorescence by restricting intramolecular rotation on the surface, a phenomenon facilitated by the entanglement of aliphatic chains from asphaltene molecules. This unique property makes them applicable in anti‐counterfeiting and determination of ethanol content in aqueous solution.