Intermingled Coordination Environments Enable Defect-Engineered Metal-Polyphenol/G-Quadruplex Hydrogel for Enhanced N2-to-NH3 Photoconversion.

Manipulating the coordination environment through hetero-ligand incorporation induces controlled defects at catalytically active sites, offering a powerful route to regulate electronic structure and reactivity. Here, we present a supramolecular approach to defect engineering within a soft hydrogel matrix by confining a Bi3+-caffeic acid complex within a guanosine monophosphate-based G-quadruplex hydrogel. This confinement not only breaks local coordination symmetry and generates oxygen-vacancy-rich heterojunctions but also emulates the active-site environments of enzymes. The G-quadruplex fibrillar scaffold provides ion-channel-like pathways that facilitate charge transport, enhance substrate diffusion, and promote selective adsorption, while confinement ensures the uniform dispersion of catalytic sites. Together, these synergistic effects result in an exceptional N2 to NH3 conversion of 905.2 µmol h-1 g-1 (cat) under visible light irradiation, 3.8 times higher than that of the pristine complex. This work introduces a versatile strategy that integrates defect engineering, heterojunction formation, and biomimetic confinement within a soft supramolecular assembly, establishing G-quadruplex hydrogels as a powerful platform for sustainable photocatalytic nitrogen fixation and beyond.