Cecil V. Francis

Materials science of organic compounds: Part 2. Thermal studies of acentric (second-harmonic-generative) and centrosymmetric crystals of achiral straight-chain para-nitrophenylcarbanyl compounds

Abstract Straight-chain alkyl and analogous polymethylene p -nitrophenylurethanes and ureas yield acentric crystals having nonlinear-optical (NLO) properties. DSC onset points are shown to agree with metal-calibrated capillary melting ranges within experimental error. Heats of fusion and melting/onset points for the alkylurethanes (C 1 -C 22 ) show a sharp minimum at C 4 -C 5 . The high second-harmonic-generation (SHG) maximum at C 6 appears unrelated. Several of the alkylurethanes (C 2 , C 5 , C 7 , and C 16 ), when crystallized using different solvents or temperatures, yielded SHG-inactive forms differing in heats of fusion, though not in onset points; in other cases lower heats of fusion upon remelting suggested analogous changes. Similar behavior was noted for some ureas and for some omega-substituted polymethylene urethanes.

Computational Modelling And Design Considerations Of Nonlinear Optical Materials

Compounds having large second-order nonlinear optical (NLO) response are those composed of suitable donor and acceptor groups in a delocalized π-system. In addition to the relative strengths of the donor/acceptor groups, the performance of a NLO compound depends also on the nature of the conjugated π-system, the molecular conformation and other geometric factors. To design better NLO materials, it is essential to have a good understanding of these factors. These molecular properties are addressed from the theoretical point of view. Their relation to NLO response will also be discussed.

Processable Cross-Linked Polymers for Nonlinear Optical Applications

Novel difunctional barbituric acid methine dyes have been synthesized for nonlinear optical applications. These Molecules have been reacted with Multi-functional isocyanates resulting in cross-linked polyurethanes. The thermal stability of the dye in crystalline form as well as dissolved in poly (Methylmethacrylate) was studied. Results suggest that although the dye crystals were thermally stable to 300 °C, when dissolved in a polymer the stability was markedly lower.

Third Order Optical Nonlinearity in a Polymer Composite

Abstract : Third-order optical nonlinearity in organic materials has generally been sought from molecules and Polymers having extended 7c-electron delocalization in conjugated bonding schemes. In an alternative approach, we have investigated the third-order optical response of a polymeric composite containing charge transfer complexes in which the nonlinearity originates from intermolecular electron delocalization between pi-electron clouds in charge transfer stacks. The material, which is composed of a polymer having electron donating pendant side groups that complex with dopant electron-acceptor molecules, has been processed into an optically clear thin film. Nonlinear characterization of the film by means of third-harmonic generation suggests enhancement of the third-order response arising from charge transfer interactions.