Observation of an optically forbidden state of C60 by nondegenerate two-photon absorption spectroscopy

Two-photon absorption (TPA) spectra of C60 in toluene were measured for a wide wavelength region from 270 to 680 nm by femtosecond pump–probe nondegenerate TPA spectroscopy. A distinct TPA band peaked at 314 nm was observed, and its intensity was evaluated to be 80 GM. The depolarization ratio of the TPA band was found to be zero within the experimental uncertainty, which indicates that this band is due to a totally symmetric (Ag) two-photon allowed excited state. The energy of the observed Ag state is about 1 eV below a prediction based on the theoretically calculated π-electron energies.