Several ladder polymer systems, such as POL and PTL, have displayed large third-order optical nonlinearities. However, these polymers are insoluble in common organic solvents, and as such are not amenable to studies of substituent effects on the nonlinear optical properties. During the past year we have developed synthetic and processing methodology to produce optical quality guest-host composites in polycarbonate, poly(methyl vinyl ether) and most recently polystyrene. In this paper we describe the synthesis of selected guest ladder 5-ring oligomers, and describe the preliminary NLO characterization as thin film composites.

Host-guest molecular composites of conjugated rigid-rod polymers in the matrix of flexible-chain polymers were prepared from blend solutions of the Lewis acid complexes of the component polymers. Molecular composites of poly(p-phenylene benzobisthiazole) (PBZT) with the polyamides Nylon 66 and PTMHT were prepared and their linear and nonlinear optical properties were investigated by optical absorption and third harmonic generation spectroscopy, respectively. Dispersion of PBZT in a polyamide matrix was found to result in reduced π-electron interactions as evidenced by the narrowing of the main absorption band. The χ(3) spectra of composites were measured in the wavelength range 0.8–2.4μm which spans the resonant and nonresonant regions. Nonresonant χ(3) at 1.9μtm was studied as a function of composite composition and linear and nonlinear dependences of χ(3) with mole fraction of PBZT were observed for nylon 66 and PTMHT composites respectively. Our findings that both χ(3) and χ(3)/α can be enhanced in molecular composites suggest that this is an important approach to optimize materials for nonlinear optics. Preliminary results of our studies of other new molecular composites of rigid-rod and ladder polymers are also discussed.

New soluble amorphous and crystalline complexes of conjugated aromatic Schiff base polymers with diarylphosphates have been prepared and their molecular and electronic structures and morphology characterized by FTIR spectra, electronic absorption spectra, differential scanning calorimetry and x-ray diffraction. The diphenyl phosphate (DPP) or di-m-cresyl phosphate (DCP) complexes of the conjugated polyimines have electronic structures and optical properties that are dramatically different from the pure polymers due to the formation of polyiminium ions on complexation. At diarylphosphate : imine ratio equal to 0.50, amorphous materials are obtained whereas highly crystalline complexes are obtained at the stoichiometric ratio. The potential of complexation in modulating and enhancing the thirdorder nonlinear optical properties of this class of polymers is demonstrated.

The structure and properties of a series of ferroelectric liquid crystal (FLC) guests possessing a tolan unit in the core are presented. The data shows that in racemic smectic C hosts, the o-nitroalkoxytolan unit can be oriented along the polar axis in the FLC thin films, affording interesting new materials for NLO applications. The data are consistent with basic expectations regarding the structure of the FLC host-guest system. There are, however, interesting deviations from expectation suggesting that for some guests there is a large and unexplained effect of host structure on the properties of doped FLC phases.

Two new types of reverse-mode polymer-dispersed liquid crystal films have been developed and successfully produced. The first was produced by UV-curing of a mixture of dual frequency addressable liquid crystal (DFALC) and UV-curable polymers under an applied voltage at a frequency lower than the crossover frequency (fc) of the DFALC. This first type is referred to as a dual frequency type. The second type was produced by injecting a liquid crystal having negative dielectric anisotropy into a specially prepared porous polymer film from which liquid crystal having positive dielectric anisotropy had previously been extracted. The type thus produced through such “negative-for-positive” substitution is referred to as a substitution type. While the dual frequency type can not be driven at a low frequency, substitution type can, which gives it a distinct advantage. Other electro-optic characteristics of the two types of films, including alignment properties of the liquid crystal molecules, are also discussed.

Carbon dioxide is used to induce glass transition in amorphous polymer films, allowing efficient alignment of chromophores with an applied electric field. The noncentrosymmetric films thus produced are capable of second harmonic generation (SHG). This method has advantages over previously investigated poling schemes, including poling at ambient temperatures and use of high glass transition temperature polymers. Several polymeric systems have been studied. The chromophrores were either dissolved in the polymer, attached as a side chain, or incorporated into the backbone of the polymer. The SHG of the films was observed as a function temperature. Of the systems studied, polyether sulfone retains SHG capability to the highest temperature. Two different systems had the greatest retention of SHG up to the glass htansition temperature. They were Poly((4-N-ethylene-N-ethylamino)- rz-cyanocinnamate), a polymer which has the chromophore incorporated in the backbone, and 4- (dimethylamino)-4'-(dimesitylboro)azobenzene, a host-guest system with a relatively large chromophore. These and other systems will be discussed.

Poly(CMPV-co-PV) have been synthesized via water soluble sulfonium salt precursor route and their linear and non-linear optical properties were characterized. The electro-optic response was stable up to 100°C when the materials were poled during the elimination. The thermal stability and mechanical strength of PPV and its derivatives, and easy processibility from the precursor polymers suggest a new approach for the molecular design of the 2nd order non-linear optical polymers.