Full temporal resolution of the two-step photoinduced energy–electron transfer in a fullerene–oligothiophene–fullerene triad using sub-10 fs pump–probe spectroscopy

The intramolecular photoinduced energy and electron transfer in a fullerene–oligothiophene–fullerene triad with nine thiophene units (C60–9T–C60) has been investigated with sub-10 fs pump–probe spectroscopy in solvents of different polarity. Photoexcitation of the oligothiophene moiety results in an ultrafast singlet-energy transfer reaction to create the fullerene singlet-excited state with a time constant of 95 fs, irrespective of the polarity of the medium. In a polar solvent, the ultrafast singlet-energy transfer is followed by intramolecular electron transfer from the oligothiophene to the fullerene with a time constant of 10 ps, resulting in a charge-separated state (CSS) with a lifetime of 80 ps.