Molecular and Crystal Engineering for Organic Nonlinear Optical Materials

Abstract Nonlinear optical crystals appear very attractive due to their potential applications in optical signal processing. We have investigated several strategies in order to get efficient organic nonlinear optical crystals having enhanced quadratic responses and, more particularly, high efficiencies for second harmonic generation (SHG). First one chooses molecules with high molecular hyperpolarizability, β. Typical molecules possess a highly delocalized π-electron system bearing a donor and an acceptor group in such positions that an intramolecular charge transfer occurs. Secondly these molecules must be assembled in an optimized acentric fashion to get a material having a high second order electric susceptibility, χ(2). The use of chirality to ensure noncentrosymmetric crystal structures, extra polar groups to influence dipole-dipole interactions, push-pull N-oxide bonds and hydrogen bonding proved to be satisfactory strategies to get some of the most efficient organic crystals for nonlinear optics : ...