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

极化聚合物的非线性光学(NLO)特性是当前科学技术研究的热点。众所周知，在介质中引入择优的发色团取向可以产生有用的二阶NLO材料。由于大多数NLO分子具有明显的静电偶极矩，这些分子可以通过高于主体聚合物玻璃化转变温度的电场来排列。然后，定向分子被冷却并以首选的排列方式冻结。极化聚合物的一个普遍问题是由于聚合物侧链的局部弛豫过程导致其非线性光学系数的衰减。为了改善这一问题，提出了具有SHG活性的对硝基苯胺(PNA)的制备新方法。尽管聚己内酯(PCL)和PNA由于其中心对称的晶体结构而不单独表现出任何二次谐波(SHG)，但两者的混合物显示出高效的倍频活性。…更重要的是，即使在没有电场的情况下，这个体系也会自发形成偏心的分子取向。从含有巨大球晶的样品中可以观察到很强的倍频效应。PNA/PCL体系呈现典型的共晶相图：液体中只有一相，固相中有两相。由于氨基和酯基之间的氢键，PNA和PCL在熔融状态下是相容的。如果客体和主体之间没有相互作用，如PNA和聚乙烯，则相在熔融状态下分离，结晶后没有倍频活性。为了得到高度烷基化的PNA晶体，必须控制成核的形成。当薄膜在晶化前进行划痕时，晶核的形成从每个划痕点开始，并垂直于划痕线生长。这种晶体生长被称为跨晶体生长。得到的d，33几乎与2-甲基-4-硝基苯胺的dll一样高。此外，该系统的长期稳定性不会衰减超过1年。因此，PNA/PCL系统为未来的技术提供了许多潜在的优势。较少

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