PHOTOTHERMAL INVESTIGATION OF THE TRIPLET-STATE OF C60

Photophysical properties of the triplet state of C60 (buckminsterfullerene) are investigated by photothermal techniques: thermal lens (TL), transient grating (TG), and photoacoustic (PA) methods. The quantum yield of singlet oxygen formation (PHI-DELTA) by the quenching of the triplet state of C60 is measured by the time-resolved TL method. The value of PHI-DELTA is nearly unity and independent of the excitation wavelength. The time dependence of the TL and TG signals does not show expected slow-rising components. This peculiar behavior can be explained in terms of a strong T-T absorption at the He-Ne laser wavelength. By using the PA method, the energy of the triplet state is determined to be 13 100 +/- 300 cm-1.