Presented in this work are initial, systematic studies of third-order nonlinear optical (NLO) susceptibilities using degenerate four-wave mixing measurements in solution at 1.064 mum and their relation with structural features for a series of poly(aromatic amines) and S-heteroatom aromatic ring-containing processible conducting polymers the syntheses of which have already been reported. These include poly(diphenylamine) and other analogues of polyaniline, poly(aminoquinolines), poly(1-aminopyrene), poly(3-aminopyridine), poly(3-aminopyrazole), poly(aminothiazoles), poly(aminothiadiazoles) and poly(isothianaphthene), among others. The effects of dopant type and level and related variables are also reported. Many of the polymers show appreciable nonlinearities, typical values of chi(xxxx)(3) being 1.3 x 10(-10) e.s.u. for poly(diphenylamine) and 2.7 x 10(-10) e.s.u. for poly(1-aminopyrene). Among other findings, it is observed that introduction of multiple fused aromatic rings in the polymer backbone very significantly enhances the nonlinearity and that lower doping levels consistently yield higher nonlinearities for all polymers observed. Polymers containing S and N heteroatoms in the same ring along the polymer chain exhibit negligible nonlinearities. The time response for all polymers is found to be faster than 40 ps. Z-scan and two-photon absorption measurements are used together with other methods to demonstrate the purely off-resonant character of the third-order nonlinear susceptibilities observed for representative polymers.
