We investigated the strongly red-shifted singlet oxygen (O-1(2)) phosphorescence spectra in an aqueous preparation of C-60 buckminsterfullerene. The similar to 10 nm red shift was associated with H2O dispersions of C-60 nanoaggregates (C-60) n that can photosensitize O-1(2) in their polarizable cores. In contrast to O-1(2) produced by the water-soluble C-60-(c-cyclodextrin) 2 complex, O-1(2) trapped inside (C-60) n was short-lived (similar to 2 -3 mu s), insensitive to solvent and O-1(2) quenchers, and did not induce photocytotoxicity. To our knowledge, O-1(2) spectrum from (C-60) n is the most red-shifted O-1(2) spectrum recorded to date and it may be used to probe the inner polarizability of carbon (nano) aggregates. Published by Elsevier B.V.