Ligand-Regulated Assembly of Cobalt-Porphyrin Metal-Organic Frameworks for Efficient Photocatalytic Singlet Oxygen Generation.

Efficiently modulating intersystem crossing (ISC) to maximize singlet oxygen (1O2) generation while simultaneously expanding framework topology remains a significant challenge in porphyrinic metal-organic framework (PMOF) design. Herein, a ligand-regulation strategy utilizing a custom-designed flexible linker, meso-tetra(4'-(3-carboxylphenyl)phenyl)porphyrin (3-TCBPP) is reported, to construct two novel cobalt-porphyrin frameworks. The extended flexibility of the ligand directs the solvothermal assembly to achieve distinct topological architectures of a 1D chain motif (QPF-11) and a rare flu topology featuring trinuclear Co3 clusters (QPF-12). Spectroscopic analyses and density functional theory calculations reveal that the paramagnetic Co(II) centers play a pivotal role in optimizing spin dynamics. The open-shell metal nodes induce substantial metal-porphyrin orbital mixing and reduce the singlet-triplet energy gap, thereby facilitating rapid ISC via spin-orbit coupling. Remarkably, despite their distinct structural dimensions and topologies, both PMOFs exhibit comparable and highly efficient catalytic performance in the photooxidation of 1,5-dihydroxynaphthalene to juglone. This comparative study reveals that the local electronic configuration of the Co(II) nodes exerts a dominant influence on the photophysical properties, enabling both frameworks to maintain high catalytic efficiency despite their distinct structural topologies. This work provides valuable insights into the structure-property relationships of PMOFs for selective photooxidation.