Modulating Solid-State Photocycloaddition Kinetics via Ligand Substituents and Crystal Structures in One-Dimensional Coordination Polymers

Understanding the kinetics of solid-state chemical reactions is critical for elucidating reaction mechanisms and enabling the rational design of functional materials. However, such investigations are often impeded by limited molecular mobility, restricted reactant interactions, and complex nucleation phenomena. In this study, we employ one-dimensional crystalline coordination polymers (CPs) as structurally ordered platforms to investigate the kinetics of [2 + 2] photocycloaddition reactions of embedded alkene substrates. By integrating nuclear magnetic resonance, fluorescence spectroscopy, laser scanning confocal microscopy, and theoretical calculations, we demonstrate that the electronegativity of substituents (-F, -Cl, -Br, -I) on carboxylate ligands strongly modulates reaction rates, with more electronegative groups accelerating the kinetics. Additionally, single-crystal CPs exhibit significantly enhanced reaction rates compared to stacked crystals, attributed to uniform light penetration and reduced spatial inhomogeneity. These findings position CPs as robust model systems for probing heterogeneous reaction kinetics and offer a new framework for understanding and optimizing olefin reactivity in solid-state environments.