Nonlinear optical studies of fullerene-arylethyne hybrids

The fullerene-arylethyne hybrids 2 and 3 were synthesized in order to investigate their NLO activities. The β values for 2 and 3 were obtained by hyper Rayleigh scattering measurements. The arylethynyl fullerenes 3a-f exhibit β values in the range 20-361 × 10^-30 esu. Interestingly, the β values for 3a,b are higher than those for 3c-f; a good correlation was obtained between the Hammett σ_p values of the para substituents of 3 and their β values. The ¹H-NMR and E_1/2 data indicate that the fullerene moieties of 3 attract electrons from the arylethynyl groups in the ground state. The β values for 2a-c are higher than those for 3a-f; the paracarborane-fullerene dyad 2c exhibits an exceptionally high β value (1189 × 10^-30 esu). The electronic characteristics of the carbon and boron clusters are discussed.