Measurement of the second order molecular hyperpolarizability of C-60(-) by nondegenerate four-wave mixing

We have determined the second order molecular hyperpolarizability gamma for the charged species C-60(-) by use of coherent anti-Stokes Raman spectroscopy (CARS) vibrational lineshape analysis. We find gamma is 2.4 (+/-1.0) X 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 gamma 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.