Observation of Two-Photon Induced Excited-State Absorption Phenomena in C₆₀ and C₇₀ Derivatives

Four fullerene dyads with different cabazole units, named a, b, c, d, were studied by using a femtosecond laser with 780 nm wavelength using Z-scan methods. Interestingly, all of them show strong two-photon induced excited-state absorption behaviors, which were observed firstly in femtosecond timescale. The values of their excited-state absorption cross-section were up to 6.07×10^?18, 7.27×10^?18, 3.86×10^?18 and 4.51×10^?18 cm^?1 for a, b, c, and d, respectively.