Nonlinear Optics of Chained-Chromophore Polymer

具有高非线性光学（NLO）特性的有机材料倾向于吸收可见光。这是一个缺陷，因为它们本身吸收二次谐波产生（SHG）光。本计画的主要目的是利用量子化学计算与分子动力学计算，设计出具有高非线性光学特性且不存在上述缺陷的新型液晶高分子。(1)用密度泛函理论研究了苯甲酸苯酯（PB）和对羟基苯甲酸（HBA）二聚体（HB）作为芳香族聚酯模型的酯键的内旋转。S键的旋转主要决定了PB分子的线性，导致PB的顺式和反式构象。由于PB的顺式构象比反式构象高7.69 kcal mol/L<-1>，因此顺式构象在标准条件下几乎没有群体。HB没有顺式构象异构体。这些与实验理解一致，即聚（对羟基苯甲酸）是O类 ...更多信息 f刚性和延伸的聚合物。(2)HBA和6-羟基-2-萘甲酸（HNA）的芳香族取代物在可见光区无吸收，但在晶相和非晶相均表现出很强的倍频活性。量子化学计算表明，HBA二聚体的二阶超极化率与对硝基苯胺的二阶超极化率相当，且随聚合度的增加而增加。芳香族聚酯的大的超极化率归因于大的电子跃迁矩。(3)通过分子动力学（MD）模拟，研究了芳香族聚酯的十聚体（十个重复单元）在水相中的最稳定的分子堆积体系。MD模拟从八种可能的堆积结构开始。其中，我们发现分子间酯羰基同向排列的极性有序结构在能量上是最有利的。这与我们以前的实验观察到的SHG强度测量是一致的。少

Organic materials with high nonlinear optics (NLO) property tend to absorb visible light. This is a deficiency because they absorb second harmonic generated (SHG) light by themselves. Main aim of this project is to design novel liquid crystalline polymers (LCP) having high NLO property without such deficiency by using quantum chemical calculations and molecular dynamics (MD) calculations.(1) The internal rotation of the ester linkage for phenyl benzoate (PB) and p-hydroxybenzoic acid (HBA) dimer (HB) as models of aromatic polyesters was investigated by using the density functional theory. The rotation of S bond, which mainly determines the linearity of the molecule, leads to the trans- and cis-conformers of PB. Since the cis-conformer of PB is 7.69 kcal mol^<-1> higher than the trans-conformer, the cis-conformer has little population at standard condition. HB does not have the cis-conformer. These agree with the experimental understanding that poly(p-hydroxybenzoic acid) is the class o … More f stiff and extended polymer.(2) The aromatic copolyester of HBA and 6-hydroxy-2-naphtoic acid (HNA) shows strong SHG-activity in the nematic phase as well as the crystalline phase in spite of no absorption in the visible region. Quantum chemistry calculations show that the second-order hyperpolarizability of the HBA dimer is comparable to that of p-nitroaniline and it increases with the degree of polymerization. The large hyperpolarizability of the aromatic polyester is ascribed to the large electronic transition moment.(3) The most stable molecular packing systems of aromatic polyester have been investigated by MD simulations performed for decamer (ten repeating units) of HBA in the nematic phase. The MD simulations were started from eight possible packing structures. Among them, we found the polar ordering structure with the intermolecular ester carbonyl groups aligned in the same direction is energetically most favorable. This is consistent with our previous experimental observation for the SHG intensity measurement. Less