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.