NONLINEAR OPTICAL-PROPERTIES OF FULLERENES AND CHARGE-TRANSFER COMPLEXES OF FULLERENES

We report the determination of the second- and third-order polarizabilities of fullernes and fullerene/N,N-diethylaniline (DEA) charge-transfer complexes by solution-phase dc electric field induced second harmonic generation measurements with 1.91-mu-m radiation. The third-order polarizabilities, <gamma>1111(-2-omega,omega,omega,0), of C60 and C70 are determined to be (7.5 +/- 2) x 10(-34) and (1.3 +/- 0.3) x 10(-33) esu, respectively. The second-order polarizabilities of fullerenes are zero due to their centrosymmetric structures. However, the formation of charge-transfer complexes with N,N-diethylaniline breaks the center of symmetry and induces second-order optical nonlinearity. The dipole projection of the second-order polarizability, beta(mu), of the C60/DEA charge-transfer complex is determined to be (6.7 +/- 2) x 10(-29) esu, assuming <gamma>1111(-2-omega,omega,omega,0) is approximately the same in toluene and DEA. With due consideration to molecular size, the optical nonlinearities of fullerenes are comparable to those of linearly conjugated organics. These initial results are encouraging enough to warrant further study of the nonlinear optical properties of fullerenes and properly substituted fullerene derivatives.