Regulation between the Delayed Fluorescence and Room-Temperature Phosphorescence of Matrix-Free Carbon Dots with the Position of the Carboxyl Substituent on the Benzene Ring

The one-step hydrothermal method using six kinds of benzoic acid derivatives and ethylenediamine as raw materials was adopted to prepare six kinds of matrix-free carbon dots (CDs). On the basis of the self-protection activation method, the prepared CDs can achieve long-afterglow emission independent of any substrate support and protection. Characterization results indicate that all of the CDs have polymer characteristics, and the polymer structure can act as a polymer matrix to protect the triplet excitons of CDs from the external environment. For the first time, the regulation between the delayed fluorescence and room-temperature phosphorescence was realized successfully by choosing the position of the carboxyl substituent on the benzene ring of the raw material. The novel method that is presented can regulate the long-afterglow type of matrix-free CDs. These CDs can be used in image encryption and information anticounterfeiting.