Side‐Chain‐Induced Interlayer Slipping in Metalloporphyrin COFs Enables Microenvironment and Spin‐State Regulation for Photocatalytic CO 2 Reduction

ABSTRACT Photocatalytic CO 2 reduction (CO 2 RR) involves a cascade of intrinsically coupled processes, rendering the independent optimization of catalytic kinetics and thermodynamics challenging. In this study, we introduce a structural regulation strategy via steric‐driven interlayer slipping engineering of metalloporphyrin‐based covalent organic frameworks (COFs) to decouple and simultaneously optimize the catalytic microenvironment and the spin state of the active metal center. Through regulating the length of alkoxy side‐chains, conventional AA stacking is transformed into a moderately serrated slipped configuration (AA*). Kinetically, the resulting slipped nanochannels enhance local hydrophobicity and spatial confinement, thereby greatly enriching in‐channel CO 2 concentration and suppressing hydrogen evolution. Thermodynamically and electronically, this interlayer slipping reconstructs the ligand field of catalytic Co sites and maximizes vertical π–d exchange interactions. As a result, this triggers a collective spin transition from isolated low‐spin ( S = 1/2) monomers to a high‐spin ( S = 3/2) state, which significantly prolongs charge carrier lifetimes and optimizes the adsorption and activation of the *COOH intermediate. Consequently, the optimized CoP‐COFs deliver a record CO production rate of 71.4 mmol g −1 h −1 with 90% selectivity among porphyrin‐based COF photocatalysts. This work establishes stacking engineering as a versatile strategy for decoupling entangled reaction steps to enable efficient solar fuel production.