The triplet properties of a series of fullerene dihydroderivatives of the o-quinodimethane type and of three representative inclusion complexes with γ-cyclodextrin and calixarenes have been studied. It is found that chemical modification results in a decrease of the singlet oxygen quantum yield relative to with an C60, average ΦΔ = 0.76. On the other hand, encapsulation in either γ-cyclodextrin or calixarene produces greatly varying results depending on host and solvent. Thus, in D2 O the γ-cyclodextrin complex of C60 sensitizes O2(1Δg) with ΦΔ = 0.77, while the calixarene complex is totally ineffective, probably due to the occurrence of a fast charge transfer-mediated deactivation process. In CCl4 the calixarene complex acts very much like C60, i.e., ΦΔ = 0.84.