The Study on Nonlinear Optical Properties in Superstructure Controlled Polymer-Dye (Guest-Host) Systems

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Nonlinear optical(NLO)properties of poled polymers are currently in the focus of intense scientific and technological interest. It is well known that introduction of a preferred chromophore orientation in a medium can create a useful second-order NLO materials. Since most of the NLO molecules have appreciable static electric dipole moments, these molecules can be aligned by an electric field above glass transition temperature of host polymers. Then, oriented molecules is cooled down and freezing in the preferred alignment. A general problem of poled polymers is the decay of their nonlinear optical coefficients due to local relaxation process of polymer side chains. In order to improve this problem, novel preparation method of SHG active P-nitroaniline(PNA)was proposed. Although Poly(epsilon -caprolactone)(PCL)and PNA do not individually exhibit any second harmonic generation(SHG)because their centrosymigetric crystal structure, but a mixture of both shows highly efficient SHG activity. … More This system spontaneously forms an acentric molecular orientation even without the application of an electric field. A strong SHG could be observed from the sample which contained huge spherulites. The pNA/PCL system shows a typical eutectic phase diagram : having only one phase in the liquid and two phases in the solid state. The pNA and PCL are miscible in a molten state due to the hyderogen bondings between amino and ester groups. If there is no interaction between guest and host, such as pNA and poly (ethylene) the phase is separated in the molten state and exhibit no SHG activity after crystallization. In order to get highly alligned PNA crystals, it is necessary to control the formation of nucleus. When the film was scratched before crystallization, the formation of nucleus start from the each scratched point and grows perpendicular to the scratched line. This kind of crystal growth is well known as transcrystal. The obtained value of d, 33 is almost as high as dll of 2-methyl-4-nitroaniline. Furthermore, the long term stability of this system doesn't decay for more than 1 year. Thus pNA/PCL systems offer a number of potential advantages to future technology. Less