【作者】 元以中；

【导师】 孙真荣；

【作者基本信息】 华东师范大学 ， 光学， 2007， 博士

【摘要】 伴随着光子时代的到来，有关全光开关、全光计算和全光通讯的理论和实验研究正日益得到重视。作为其中重要的信息载体，三阶非线性光学材料在上述领域的应用价值目前已引起越来越广泛的关注。与传统的无机材料相比，有机及金属有机三阶非线性光学材料具有非线性光学系数高、响应时间快、介电常数低和良好的可加工性等无可比拟的优点，因而在上述全光器件的开发中扮演着重要的角色。然而遗憾的是，当前有关有机及金属有机三阶非线性光学材料的分子设计和材料加工方面的研究在深度和广度上仍十分有限。基于此，本文分别设计、合成了两类代表性的新型有机及金属有机分子——芳杂环取代多甲川花菁和咔唑羰基铬配合物。在此基础上，按照分子非线性光学研究中的“分子工程”和“材料工程”原理，从实验和理论两方面对它们的三阶非线性光学及其相关特性进行了系统而深入地考察，取得了若干有意义的研究结论。具体研究内容和结果如下：（1）设计、合成了五个芳杂环取代多甲川花菁染料和三个咔唑羰基铬配合物，利用元素分析、质谱、红外光谱、核磁共振氢谱对它们的分子结构进行了充分确证。还进一步利用X-射线单晶衍射技术获得了其中两个咔唑羰基铬配合物的详细晶体学数据；（2）借助紫外一可见吸收光谱和荧光光谱研究了上述八个化合物的线性光学特性，获得了它们的分子电子态结构和能级分布的相关信息。结果表明两类分子在可见光区具备良好的透明性。对咔唑羰基铬配合物还观察到了来自金属到配体的电荷转移特征吸收带；（3）采用皮秒前向简并四波混频技术测试了所有目标分子的三阶非线性极化率、二阶超极化率以及非线性折射率等非线性光学参数。测试结果表明，芳杂环取代多甲川花菁染料具有相当强的非共振三阶非线性光学响应，其二阶超极化率γ值达到10^-29esu量级，表明多甲川链中芳杂环取代基的引入对分子三阶非线性光学性能的提高起着重要的作用；（4）引入简化的自由电子模型和含时微扰理论对芳杂环取代多甲川花菁染料的分子结构和三阶非线性光学性能间的关系进行了进一步讨论，研究表明适当增加甲川链的长度、引入重原子取代以及增加两端芳杂环取代基的电负性差值以提高分子的永久偶极矩是进一步提升花菁染料γ值的一个有效途径；（5）对咔唑羰基铬配合物，研究发现铬金属配位可大大增强原有机配体的三阶非线性光学响应，产生上述现象的原因是由于配合物分子中金属到配体的低能电荷转移跃迁。此外，结合含时微扰理论和密度泛函理论计算，对引起咔唑羰基铬配合物三阶非线性光学性能差异的物理机制进行了深入探讨。结果表明，除金属到配体的低能电荷转移跃迁外，羰基铬配位位点不同导致的分子电子波函数空间分布的不一致性是影响其三阶非线性光学性能的另一重要途径。这一结论为今后新型金属有机非线性光学材料的分子设计提供了一个值得借鉴的思路；（6）利用简单的旋涂技术成功地构筑了三个芳杂环取代多甲川花菁染料的J-，H-，和Herringbone型有序分子聚集体超薄膜，借助紫外一可见吸收光谱、红外光谱、小角X-射线衍射、原子力显微和椭圆偏振等现代光谱和形貌表征技术对上述超薄膜的聚集态结构和形貌进行了精确的确证。借助前向简并四波混频技术测试了它们的三阶非线性光学参数，结果表明薄膜的三阶非线性光学性能得到了大幅度的非共振增强。在此基础上，分别应用一维共线理想谐振子理论和CEO理论详细分析了引起这种增强的内在机制，研究发现上述超薄膜的三阶非线性光学响应来自外场激励下光生激子在分子聚集体空间的非谐振动且聚集体微结构的有序性和分子密度的增加可有效促进了光生激子运动的自由度和相干性，从而对三阶非线性光学效应的提高起到积极的贡献；（7）同样利用旋涂技术成功制备了一个咔唑羰基铬配合物的H-聚集体超薄膜，借助紫外—可见吸收和荧光光谱初步确定了它的结构。利用前向简并四波混频技术首次发现该超薄膜具备相当大的非共振三阶非线性极化率(x^（3）=4.21×10^-12esu)，与之相关的机理研究正在进行中。更多还原

【Abstract】 With the advent of photonic age, the theoretical and experimental researches on all-optical switching, all-optical computing and all-optical communication have become more and more important. As a key information media among them, the application of materials with excellent third-order nonlinear optical （NLO） properties has also received more interests. Compared with inorganic crystals, third-order NLO-active organic and organometallic molecules have become prominent candidates to be developed as novel all-optical devices for their high nonlinear optical susceptibility, fast nonlinear optical response time, low dielectric constant, and good tailorability. Unfortunately, the studies on the molecular design and material processing of organic and organometallic third-order nonlinear optical materials are still extensively and intensively preliminary.In this thesis, two series of organic and organometallic molecules, polymethine cyanines endcapped with different heterocyclic groups, and carbazole derivatives coordinated with carbonyl chromium moieties, were well-designed and synthesized. Based on the "molecular and material engineering" approach, the systematic and thorough investigations on the structural dependences of their third-order nonlinear optical properties were carried out from both theoretical and experimental point of views, and some interesting results have been unraveled as the following:（1） Five polymethine cyanines endcapped with different heterocyclic groups and three carbazole derivatives coordinated with carbonyl chromium moieties were designed and synthesized, and their molecular structures were characterized by element analysis, mass spectra, infrared spectra, and nuclear magnetic resonance, and the detailed crystallographic data of two carbonylchromium - complexed carbazole derivatives were successfully acquired by X-ray diffraction.（2） The linear optical properties of the above-mentioned compounds were studied by UV-visible absorption and fluorescence spectroscopy, and their molecular electronic structure and the distribution of their energy levels were revealed. The results indicate that they all possess good optical transparency in visible region. For carbonylchromium - complexed carbazole derivatives, the characteristic absorption bands originated from metal-to-ligand charge transfer transition can be clearly observed.（3） The nonlinear optical parameters, including their third-order nonlinear susceptibilities, their second-order hyperpolarizabilities and their nonlinear refractive indexes, were systematically measured by pico-second degenerate four-wave mixing technique, and the off-resonant y values of about 10^-29 esu were obtained in the polymethine cyanines, which was attributable to the introduction of heterocyclic fragments.（4） The dependences of third-order optical nonlinear on the molecular structures of polymethine cyanines were thoroughly analyzed by introducing the simplified free electron model and the time-dependent perturbation theory. It suggested that the molecular y values can be effectively improved by lengthening the polymethine chain, the substitution of heavy atoms, and increasing the molecular permanent dipole moment by increasing the electronegative difference between the endcapped heterocyclic groups.（5） The coordination of chromium center was observed to dramatically improve the molecular third-order optical nonlinearities in the carbonylchromium - complexed carbazole derivatives, and it could be attributable to the metal-to-ligand charge transfer transition with the low energy gap. Based on the time-dependent perturbation theory and density functional theory, it could be further deduced that the different molecular conformation would induce the different spatial distribution of the molecular electronic wave function, and therefore result in the different third-order optical nonlinearities, which provides an effective guideline for the rational molecular design towards novel organometallic nonlinear optical chromophores;（6） A series of well-ordered J-, H-, and Herringbone-type aggregate ultrathin films of three polymethine cyanines were successfully achieved by spin-coating technique. Their structural and morphological characters were confirmed by UV-visible spectra, infrared spectra, small-angle X-ray diffraction, atomic force microscopy, and ellipsometry. Their third-order optical nonlinearities were also measured by forward degenerate four-wave mixing technique, and the off-resonant enhanced third-order nonlinear optical susceptibilities were observed. Their mechanisms were elaborated based on one-dimensional linear oscillator model and collective electronic oscillator （CEO） theory, and it implied that there was a strong correlation between their third-order NLO behaviors and optically driven aharmonic oscillations of photoexcitons confined in molecular aggregates, and the freedom and coherence of the photoexciton motion were augmented in the ordered molecular self-organization processes and have the positive contributions to the largely enhanced third-order optical nonlinearities.（7） A H-aggregate ultrathin film of carbonylchromium - complexed carbazole derivative was also prepared by spin-coating technique. Its structure was basically characterized by UV-visible and fluorescence spectra. The considerable third-order optical nonlinearity (X^（3）= 4.21×10^-12 esu) of the film at the off-resonance wavelength （532 nm） was first observed by forward degenerate four-wave mixing technique. The research on the physical origin of the corresponding third-order optical nonlinearity is in progress.更多还原