Side-Chain-Induced Interlayer Slipping in Metalloporphyrin COFs Enables Microenvironment and Spin-State Regulation for Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction (CO2RR) 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 CO2 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.