CHI(3) DISPERSION MEASUREMENTS OF THE CONJUGATION LENGTH DEPENDENCE OF CAROTENOID DERIVATIVES

The dependence of the nonlinear susceptibility, chi(3), on conjugation length has been investigated by third harmonic generation measurements of four astaxanthene molecules (carotenoid derivatives). These polyenes contain 5-17 double bonds and were synthesized and prepared as thin films by spin coating. Measurements, from 1 to 2.5 mum, revealed chi(3) to be linearly dependent on conjugation length, reaching a maximum of 1.2 x 10(-10) esu for the longest chain astaxanthene. In contrast to beta-carotene, the three-photon resonance extends over a greater wavelength range to yield an enhanced figure of merit chi(3)/a almost-equal-to 10(-12) esu-cm. Extrapolation of these results to polyacetylene is analyzed.