The effect of fullerene aggregation on nonlinear optical properties of solutions

Experimental data on the concentration dependence of nonlinear third-order optical susceptibility of fullerene C-60 in benzene solution are analyzed. The deviation of the dependence from a linear behavior is attributed to the fullerene aggregation phenomenon in solution investigated previously. The aggregation shifts the four-photon resonance frequency. It is inferred from a comparison of the size distribution function of fullerene clusters in so lution calculated previously based on the drop model of clusters with the e xperimental chi((3))(C) dependence that fullerene molecules incorporated in clusters do not virtually experience resonant four-photon interaction, so that the nonlinear optical response depends only on isolated molecules C, i n the solution studied. The possibility of utilizing the nonlinear optical characteristics of fullerenes in solutions in studies of their aggregation is discussed.