Photochemical N‐dealkylation of Tertiary Amines Coupled With Photocharging of Poly(Heptazine Imides)

ABSTRACT Photocharging in carbon nitride materials is emerging as a promising route for light‐driven energy storage, yet the nature of the storage sites and their mechanisms remain elusive. Here, we investigate photocharging in poly(heptazine imide) (PHI), focusing on its protonated (H‐PHI) and sodium (Na‐PHI) forms. Using the photochemical dealkylation of triethylamine, we quantify the density of electron–proton (e − /H + ) pairs stored in these materials and define a descriptor, N e : N hept , to track photocharging at the molecular level. H‐PHI demonstrates superior electron storage and reactivity, attributed to its microporous 2D structure and favorable energetics. Theoretical modeling, combined with spectroscopic analysis, reveals the nature of the active heptazine sites and their transformation during charging. The material retains its structural and functional integrity across multiple cycles, underscoring its stability and recyclability. These insights open new avenues for the rational design of carbon nitride‐based semiconductors for light‐induced redox applications.