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 (C60 or C70) 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.