High-reactivity precursor C₂N₃H and its photo-induced stepwise growth toward 2D graphitic carbon nitride clusters

To investigate the precursors and growth mechanisms of two-dimensional C_xN_y materials, we performed laser ablation mass spectrometry and spectroscopy on graphitic carbon nitride. A series of clusters, [(C₂N₃)_nH_n-1]^- (n = 1-4), were identified, with C₂N₃ ^- as the dominant species. Structural analyses indicate that C₂N₃H is a linear molecule containing cyanide and carbodiimide groups, whereas C₂N₃ ^- corresponds to a dicyanamide anion. Their reaction sites, characterized by a three-center four-electron motif and electron delocalization, promote polymerization. C₄N₆H^- forms via C₂N₃H + C₂N₃ ^- coupling, and C₆N₉H₂ ^- is generated through a two-step cyclization involving two C₂N₃H and one C₂N₃ ^-. Theoretical results predict that fused-ring C₈N₁₂H₃ ^- can evolve from C₄N₆H^- with two C₂N₃H, or from C₆N₉H₂ ^- with one C₂N₃H. This progression from linear to branched, cyclic, and fused-ring clusters parallels g-C₃N₄ growth, suggesting a synthesis route for 2D C_xN_y materials and providing insights for detecting nitrogen-rich carbon clusters in interstellar space.