Efficiency of singlet oxygen production from self-assembled nanospheres of molecular micelle-like photosensitizers FC4S

Abstract

Direct detection of singlet oxygen (¹O₂) production under irradiation of molecular micelle-like hexa(sulfo-n-butyl)[60]fullerene (FC₄S) self-assembled nanospheres at 500–600 nm was obtained by the measurement of its near-infrared luminescence at 1270 nm. This photocatalytic effect makes FC₄S a potential alternative sensitizer to TiO₂ and feasible for use in the visible region in addition to its intrinsic high UV efficiency. Despite having a relatively low optical absorption of FC₄S at 600 nm, appreciable ¹O₂ signal was detected comparable to that of hematoporphyrin derivatives Photofrin at the same molar concentration, but less than sulfonated aluminium phthalocyanine, AlS₄Pc. The quantum yield of FC₄S for the generation of ¹O₂ in H₂O was roughly estimated to be 0.36 using the relative correlation to that of C₆₀/γ-CD. The absolute value is not available. These results demonstrated efficient triplet energy transfer from ³FC₄S* to molecular oxygen in the nanosphere structure. We also confirmed certain retention between photocatalytic characteristics of underivatized C₆₀ with that of FC₄S, a C₆₀ hexaadduct containing a single covalent bond between each addend and the fullerene cage, in contrast to other Bingel-type hexamalonate adducts of C₆₀ in the literature with a low ¹O₂ yield.