Synthesis and photophysics of a fullerene-triquinoxaline ensemble

In this contribution, we report the synthesis and photophysical characterization of a molecular conjugate, in which C(60) is covalently attached to a triquinoxaline-based cavitand through a pyrrolidine ring. Comparative experiments performed by using suitable model compounds demonstrate negligible interactions between the quinoxaline chromophores and the fullerene centre in the ground state. On the other hand, fluorescence emission and excitation spectra provide evidence for the occurrence of efficient photoinduced singlet-singlet energy transfer from the quinoxaline moiety to the C(60) core. Laser flash photolysis experiments show that such an intramolecular process precludes the population of the lowest triplet state of the quinoxaline. By way of contrast, the lowest triplet state of the fullerene is effectively populated and is capable of sensitizing the formation of singlet oxygen in high yield, as unambiguously demonstrated by its typical infrared phosphorescence, detected by using time-resolved luminescence apparatus. The fullerene-quinoxaline conjugate exhibits photoinduced DNA-cleaving activity, as confirmed by preliminary photocleavage experiments carried out with a pBR322 supercoiled plasmid.