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 measurement s of four astaxanthene molecules (carotenoid derivatives). These polye nes contain 5-17 double bonds and were synthesized and prepared as thi n 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 wa velength range to yield an enhanced figure of merit chi(3)/a almost-eq ual-to 10(-12) esu-cm. Extrapolation of these results to polyacetylene is analyzed.