Singlet oxygen generation properties of an inclusion complex of cyclic free-base porphyrin dimer and fullerene C₆₀

To gain insight into the singlet oxygen (¹O₂) generation properties of supramolecular complexes of cyclic free-base porphyrin dimer with fullerene C₆₀, we evaluated the ¹O₂ quantum yield (Φ_Δ) and rate constant (K_obs) of ¹O₂ generation for a cyclic free-base porphyrin dimer (CPD) linked by butadiyne bearing four 4-pyridyl groups and its inclusion complex (C₆₀⊂CPD) with C₆₀. We demonstrate that CPD and C₆₀⊂CPD possess the ability to generate ¹O₂ under visible light irradiation. Moreover, it was found that the Φ_Δ value of C₆₀⊂CPD is lower than that of CPD. Based on the kinetic and thermodynamic consideration concerning the electron transfer processes between the porphyrin dimer and C₆₀, this work revealed that the lower Φ_Δ value of the C₆₀ inclusion complex would be attributed to the formation of the charge-separated state c₆₀^·−-CPD^·+, leading to a low intersystem crossing (ISC) efficiency for the formation of the triplet excited state ³(CPD)*.