DISPERSIONS OF ELECTROABSORPTION SUSCEPTIBILITIES - APPLICATION TO A POLYMERIC LANGMUIR-BLODGETT-FILM

The relation between the dispersions of nonlinear optical susceptibili ties chi((n))(omega;omega,0,...,0) and chi((n-1))(omega;omega,0,...,0) (for electro-optic process) of organic polymeric materials is studied based on the premises that the microscopic polarizabilities alpha, be ta, gamma, delta, ... are derivatives of their next lower order polari zabilities, with respect to the effective internal field F across the polarizable pi-conjugated systems, and that these derivative relations hips are still valid when dynamic (frequency-dependent) processes are considered. Electroabsorption spectroscopy has been used to determine the dispersion of chi(113)((2)) and chi(1133)((3)) of a polyamic acid salt Langmuir-Blodgett film containing covalently bonded azobenzene NL O chromophores. The results are consistent with our prediction, and co nfirm the validity of the derivative relationships proposed by Marder et al. [Science 265 (1994) 632; J. Am. Chem. Soc. 116 (1994) 10703]. T his LB film also gives appreciable values of both chi(113)((2)) (26 pm /v) and chi(1133)((3)) (2 X 10(-11) esu). (C) 1997 Elsevier Science B. V.