Positional Effects of Single-Atom Active Sites in 1D Porphyrinic COFs on Photocatalytic CO2 Reduction.

The selective photocatalytic reduction of carbon dioxide (CO2) to methane (CH4) remains a formidable challenge due to the demanding eight-electron/proton-coupled reduction process. Here, we report a positional engineering strategy for tailoring the spatial distribution of single-atom active sites within 1D porphyrinic covalent organic frameworks (CPOF-13-M1-M2, where M1 = H/Cu and M2 = H/Cu), enabling tunable catalytic selectivity. By selectively positioning Cu atoms at either edge- or central-positioned porphyrin sites of the framework, or both, we elucidate how active-site location governs charge-carrier dynamics and reaction pathways. Central Cu sites favor CO formation via *CO desorption, whereas edge-positioned Cu sites promote sequential hydrogenation of *CO toward CH4 through multielectron transfer, achieving a CH4 production rate of 31.6 µmol g-1 h-1 with 92.9% electron selectivity. Dual-site configurations exhibited intermediate selectivity, reflecting the competing catalytic preferences of the two differently positioned active sites. These findings establish active-site positional engineering as a versatile design principle for tailoring photocatalytic pathways in COF-based catalysts, opening new avenues for the rational design of reticular materials for solar fuel generation.