Discovering the polymerization mechanism of aromatic carbon nitride†

Abstract

Aromatic carbon nitride (PhCN) has become an important luminescent material due to its excellent optical properties and has attracted attention in photoluminescence and electroluminescence applications. Normally, PhCN is synthesized by thermal polymerization of 2,4-diamino-6-phenyl-1,3,5-triazine (DPT). However, the polymerization mechanism is still unclear. Here we investigated the polymerization process of 2,4-diamino-6-phenyl-1,3,5-triazine (DPT) at different temperatures. The results indicate that at 350 °C, DPT decomposes into benzonitrile and cyanamide; the phenyl group does not participate in polymerization and the cyanamide polymerizes into melem. As the temperature increases to 370 °C, the phenyl group gradually engages in polymerization, while the generation of melem diminishes and eventually ceases at 410 °C. The characterization of its optical properties indicates that the phenyl substituent leads to an increase in the degree of conjugation and promotes π-electron delocalization, resulting in a redshift in the UV-vis absorption and PL spectra. This work provides foundational insights into the synthesis, structure, and optical properties of PhCN, which are expected to facilitate further exploration and broader applications.