Quantitative transduction of excited-state energy in fluorophore-heterofullerene conjugates

Abstract A novel series of fluorophore‐heterofullerene conjugates 10 – 14 — the fluorophores range from benzene, naphthalene, phenanthrene, and fluorene to pyrene — was synthesized. NMR spectroscopy and quantum mechanical calculations demonstrate that the flexibility of the acetyl‐group linker opens the way for conformations with π–π stacking interactions between the chromophores. This leads to favorable electronic communication between the two subsystems and is reflected in a series of ground‐ and excited‐state assays ranging from fluorescence to fast transient absorption measurements. It was found that a common deactivation process of the photoexcited fluorophores takes place, namely, a quanti‐tative transduction of singlet excited state, yielding the hetero‐fullerene singlet excited state. This reaction pathway leads to the long‐lived and highly reactive fullerene triplet state, which forms, in a reaction with molecular oxygen, a cytotoxic oxygen species (i.e. singlet oxygen). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)