Imine‐Orientation and Confinement‐Engineered Programming of Polyiodide Speciation in Nitrogen‐Rich COFs for Tailored Iodine Capture

ABSTRACT Achieving precise control over the aggregation state of volatile iodine (I ₂ ) within porous adsorbents is critical for developing high‐performance materials that go beyond mere capacity metrics. Herein, we report a rational design strategy for covalent organic frameworks (COFs) in which polyiodide speciation is programmed through meticulous manipulation of nitrogen site environments and spatial confinement. Two nitrogen‐enriched COFs, Py‐Trz‐COF‐1 and Py‐Trz‐COF‐2, are constructed with deliberate imine orientation and interlayer slippage. Despite nearly identical topologies and comparably high iodine uptake (5.0 vs. 4.7 g·g ⁻¹ ), they exhibit distinctly different confined iodine chemistry. Comprehensive spectroscopic analyses reveal that Py‐Trz‐COF‐1 stabilizes a higher proportion of I ₃ ⁻ species, whereas Py‐Trz‐COF‐2 favors I ₅ ⁻ formation. Density functional theory calculations attribute this divergence to site‐specific electronic modulation: in Py‐Trz‐COF‐1, localized electron density at the terminal imine nitrogen enhances charge transfer and stabilizes I ₃ ⁻ , while in Py‐Trz‐COF‐2, enhanced π‐delocalization around the pyridine‐triazine cavity, coupled with larger confinement space, promotes the evolution toward I ₅ ⁻ . This work demonstrates that polyiodide distribution in COFs can be deliberately engineered through structural precision at the molecular level, offering a new design paradigm for tailoring iodine chemistry in porous materials.