Measurement of the second order molecular hyperpolarizability of C60− by nondegenerate four-wave mixing

We have determined the second order molecular hyperpolarizability γ for the charged species C60− by use of coherent anti-Stokes Raman spectroscopy (CARS) vibrational lineshape analysis. We find γ is 2.4 (± 1.0) × 10−33 esu, a value that is >65 times larger than the corresponding value for the neutral species and is comparable to values for highly conjugated organic polymers like polydiacetylene. The observed increase in γ with addition of charge to the fullerene cage has encouraging implications for the use of charge-transfer and endohedral fullerene complexes in future photonics devices.