Synthesis and fluorescence properties of [60] and [70]fullerene-coumarin dyads: Efficient dipole-dipole resonance energy transfer from coumarin to fullerene

New [60] and [70]fullerene-coumarin dyads were prepared by covalently linking a coumarin dye to a fullerene (C-60 or C-70) via a 1,3-dipolar cycloaddition reaction of azomethine ylides or by a cyclopropanation reaction of fullerenes with malonate derivatives. These dyads were spectroscopically characterized and their fluorescence properties studied. Fluorescence quenching of the coumarin fluorophore in the dyads results from efficient dipole-dipole resonance energy transfer from the coumarin moiety to the fullerene moiety.