C60 Fullerene-based materials as singlet oxygen O2(1Δg) photosensitizers:: a time-resolved near-IR luminescence and optoacoustic study

The triplet properties of a series of fullerene dihydroderivatives of the o-quinodimethane type and of three representative inclusion complexes with gamma -cyclodextrin and calix[8]arenes have been studied. It is found that chemical modification results in a decrease of the singlet oxygen quantum yield relative to C-60, with an average Phi (Delta)=0.76. On the other hand, encapsulation in either gamma -cyclodextrin or calix[8]arene produces greatly varying results depending on host and solvent. Thus, in D2O the gamma -cyclodextrin complex of C-60 sensitizes O-2((1)Delta (g)) with Phi (Delta)=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 C-60, i.e., Phi (Delta)=0.84.