Covalently linked water-soluble fullerene–fluorescein dyads as highly efficient photosensitizers: Synthesis, photophysical properties and photochemical action

The synthesis, photophysical and photodynamic properties of two water-soluble hybrid structures based on the polycationic or polyanionic fullerene [60] derivative covalently linked to fluorescein are described. The significant influence of electrostatic charges on the conformation of the studied fullerene–fluorescein structures in aqueous solution and on their photophysical properties and photochemical activity was demonstrated. A polycationic fullerene derivative–fluorescein conjugate exhibits a pronounced quenching of fluorescence (more than 25 times) due to the energy and/or electron transfer from dye to fullerene. Such activation of fullerene generates reactive oxygen species greater than 15 times more effectively than an individual dye or fullerene does. In contrast, for the polyanionic fullerene derivative–fluorescein conjugate such effects are practically absent. The demonstrated effects open up wide opportunities for a directional design of highly efficient water-soluble photosensitizers by combining the singlet-excited dyes and fullerene [60] for applications in photodynamic therapy.