Constructing Dinuclear Cd2-Porphyrin Motifs in Metal-Organic Frameworks to Accelerate Intersystem Crossing for Boosting Photocatalytic Aerobic Oxidation

Dinuclear metalloporphyrin cores remain elusive in metal-organic frameworks (MOFs), despite their potential to direct spin-orbit coupling and triplet sensitization for efficient singlet oxygen (1O2) generation. Herein, we report a structurally precise series of Cd-porphyrin MOFs to elucidate how porphyrin-core nuclearity and coordination geometry influence 1O2 photosensitization. Solvothermal regulation affords three crystalline porous frameworks featuring a free-base porphyrin core (QPF-8), a mononuclear Cd-porphyrin unit (QPF-9), and a dinuclear Cd2-porphyrin motif (QPF-10). QPF-8 serves as an additional free-base reference, whereas the closely related QPF-9 and QPF-10 provide a direct platform for probing how mono- and dinuclear porphyrin coordination environments influence photophysical properties. QPF-10 exhibits a measured 1O2 quantum yield of 0.68, compared with 0.50 for QPF-9. Spectroscopic analyses and theoretical calculations associate the dinuclear motif with enhanced metal-porphyrin orbital mixing and a 4.59-fold increase in the calculated S1-T1 spin-orbit coupling matrix element (from 3.14 to 14.40 cm-1), supporting more effective triplet photosensitization. Consistent with these photophysical properties, QPF-10 demonstrates superior catalytic activity in the aerobic photooxidation of 1,5-dihydroxynaphthalene. Notably, its activity is approximately twice that of the archetypal PCN-224(Zn) and also exceeds that of the Pt-based QPF-1(Pt). These results identify dinuclear porphyrin coordination as a structural strategy for enhancing triplet photosensitization in crystalline heterogeneous catalysts.