Local Cross-Linking Structure Regulates Active Site Mobility and Molecular Accessibility in Polymer-Bound Photocatalysts

Engineering reaction microenvironment in immobilized molecular catalysts is essential for programmable catalytic performance. Herein, we introduce a molecular strategy to regulate the reaction microenvironment based on cross-linking structure of polymer-bound catalysts. A series of polymer-bound tris(2,2′-bipyridine)Ru(II) complexes are synthesized by systematically varying the number and position of covalent anchor points between the Ru complex and polymer chains. Photoluminescence lifetime and absolute quantum yield measurements reveal that increasing the covalent anchors progressively suppresses structural mobility of the Ru core. Stern-Volmer quenching analysis shows that excessive local cross-linking lowers diffusional accessibility of dissolved O2 to the Ru complex due to sterically hindered polymer network. We elucidated that photocatalytic kinetics in a 1O2-mediated anthracene oxidation are determined by both the catalyst mobility and molecular accessibility, which correlates with energy transfer probability from a photoexcited Ru complex to dissolved O2. These findings identify the local cross-linking structure surrounding the active site as a molecular design parameter for engineering the reaction microenvironment in immobilized catalysis.