【作者】 韩莉坤；

【导师】 蒋亚东；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2008， 博士

【摘要】 随着信息技术的飞速发展，非线性光学材料在高速光通讯，光信息处理以及光学存贮等领域有着广泛的应用前景。与无机晶体相比，有机二阶非线性光学材料具有非线性系数高、响应速度快、易加工、结构可设计等优点，已经成为非线性光学与材料领域的一大研究热点。到目前为止，获得可以满足实用化要求的具有宏观非对称结构和高稳定性的有机聚合物材料，仍然是材料科学家们面临的巨大挑战。本文简要介绍了非线性光学的基本原理与应用，以及发色团的分子设计理论，着重评述了有机非线性光学材料的种类、制备技术及其研究进展。在此基础上，设计了新型发色团分子并研究了其光物理特性，制备研究了掺杂型极化聚合物膜和具有较高热稳定性的非线性光学自组装多层膜。论文主要内容包括以下几个方面：1．设计、合成了一种带有新型吸电子体D-π-A结构的三腈基二氢呋喃型发色团分子（DCDHF-2-V），并首次研究了其光物理特性。采用UV1700紫外可见分光光度计和F-4500荧光分光光度计，分别研究了该化合物在不同极性溶剂以及薄膜状态下的吸收光谱和荧光光谱特性。结果表明，随溶剂极性的增大，谱带的峰值大幅度红移，呈现明显的正溶致变色现象。在薄膜状态下发色团分子的吸收峰和荧光发射峰与溶液状态时呈现明显不同，这是由于分子聚集状态的改变和光异构化现象所造成的。研究了发色团分子在不同溶剂中的荧光量子产率以及Stocks位移的变化规律。在此基础上计算出DCDHF-2-V分子激发态与基态跃迁偶极矩之差△μ_eg=33．09×10^-30C·m，并根据双能级模型确定了分子的二阶非线性极化率β随波长的变化情况，当激光基频波长为1064 nm时，β=3323．4×10^-40m⁴/V。同时采用示差扫描量热法（DSC）和热失重分析法（TGA）研究了DCDHF-2-V分子的热性能。2．将新型发色团分子DCDHF-2-V掺入到光学性能良好的聚甲基丙烯酸甲酯（PMMA）中，采用旋涂法制备了掺杂型聚合物光学膜并讨论了膜厚随溶液浓度和旋膜转速的变化规律。研究了发色团分子掺杂含量对膜透光率的影响。采用光谱椭偏仪（Ellipsometer）测量了薄膜折射率随波长的变化情况。研究了PMMA和掺杂型聚合物DCDHF-2-V/PMMA的热性能，并采用Achar方法和Coats-Redfern方法对掺杂型聚合物DCDHF-2-V/PMMA的热降解过程的动力学过程进行了分析。为了得到宏观的二阶非线性响应，利用电晕极化方式，使聚合物膜中的极性分子沿电场方向有序排列，形成宏观的非中心对称。用原子力显微镜和紫外可见分光光度计研究了极化前、后聚合物膜的表面形貌和吸光度的变化。结果表明，极化前聚合物膜表面平整、均匀；极化后聚合物膜表面沿电场方向形成很多尖峰，且膜表面的粗糙程度与极化电压有关。同时根据吸光度的变化可以计算发色团分子的有序度Φ。采用二次谐波法测试了不同掺杂浓度下，极化聚合物膜的二阶非线性光学系数d₃₃，研究了二阶非线性光学系数d₃₃和d₃₁的关系，考虑到由发色团分子在倍频光波长处吸收造成的损耗对d₃₃进行了修正。采用同样方法制备和研究了另一种新型发色团分子的PMMA基掺杂型极化聚合物。3．通过Friedel-Crafts烷基化反应将新型发色团分子DCDHF-2-V引入聚合物的侧链，合成了含三氰基二氢呋喃结构单元的聚合物材料，并对其非线性光学性能做了初步研究。结果表明，与掺杂型聚合物膜DCDHF-2-V/PMMA相比，虽然材料的二阶非线性系数下降了，但其二阶非线性光学稳定性有了明显提高。4．以偶氮型聚阴离子PAZO为发色团分子，与感光型聚阳离子重氮树脂DR进行层层静电自组装，制备具有二阶非线性光学特性的多层组装膜，并采用紫外可见光谱跟踪成膜过程。经过紫外光照，层间的静电相互作用转化为共价酯键连接。对制备的DR/PAZO多层组装膜进行的二阶非线性光学性质、热稳定性及抗溶剂刻蚀能力的研究表明，膜层具有较明显的二次谐波信号，同时曝光后的膜层比未经曝光膜层表现出了更好的热稳定性和抗溶剂稳定性。5．以掺杂型极化聚合物DCDHF-2-V/PMMA为芯层材料，以紫外光固化聚合物材料为包层材料制备了倒脊型单模光波导，并模拟了波导的折射率分布和模场分布，并对M-Z型电光调制器进行了初步研究，完成了从材料的设计、制备、表征到应用的整个过程，为制作聚合物波导强度调制器的原型器件提供了实验基础。更多还原

【Abstract】 With the rapid development of information technology, nonlinear optical （NLO） materials have been of great interest due to their potential applications in the fields of optical information processing, optical sensing, and telecommunications. The advantages of organic NLO materials in contrast to inorganic crystals include higher NLO susceptibility, ultra-fast response characteristics, easier processing into thin films and compatibility with microelectronic processes. It is still considered to be a challenge for researchers to prepare novel polymer lattices with macroscopically non-centrosymmetric structure in which chromophoric dipolar molecules are well arranged with orientation.In this desertation, the basic theories of NLO and molecular design are briefly introduced, and the species, the preparation as well as the research progress of second order NLO materials are also summerized. Based on the preliminary investigation, a novel chromophore was synthesized and the spectroscopic properties of it were investigated. The poled polymer films were prepared and the strip waveguide using it was fabricated successfully. A multilayer NLO assembly film was prepared. The main research results were as follows:1. A second-order NLO chromophore （DCDHF-2-V） with a novel electron acceptor was synthesized. The spectroscopic properities of the chromophore in the different polar solutions and polymer matrix were investigated by the absorption spectra and fluorescence emission spectra. It is found that the absorption and fluorescence maxima are largely red-shifted along with the increase of the solvent polarity, which means that the dipole moment of the DCDHF-2-V molecule is higher in the excited state than in the ground state. The absorption spectrum and fluorescence spectrum of the film is quite different from that of the chromophore in the solution. These spectral effects arise from the difference in the aggregate state of DCDHF-2-V molecules and photoisomerization process of DCDHF-2-V molecules in a PMMA matrix respectively. The fluorescence quantum yield and Stocks shift change along with the variation of the polarity of solvent. And the difference in the dipole moment between the ground and the excited states was obtained as 33.09×10^-30C·m. The second order polarizability value of DCDHF-2-V was estimated based on the quantum-mechanical two-level model and the calculated value was 3323.4×10^-40 m⁴/V at the wavelength of 1064 nm. The thermal behavior of the chromophore was investigated by thermogravimetric analysis （TGA） and differential scanning calorimeter （DSC）, respectively.2. Spin-coated films of poly methyl methacrylate （PMMA） doped with DCDHF-2-V were fabricated. The refractive index of the polymer film was measured by an ellipsometer. With the increase of DCDHF-2-V moleculars concentration, the absorbance of the film is also enhanced. The thermal stability of the polymer （DCDHF-2-V/PMMA） was investigated by thermal gravimetry and the kinetic parameters of the degradation processes were calculated. The alignment of the NLO chromophore of the polymeric thin film was carried out by corona poling method. Domain structures of NLO-chromophores for the poled film were obtained using atomic force microscopy （AFM）. The surface of the film sample before poling is flat and this good quality film was dramatically changed after poling, resulting in numerous hills and valleys that were aligned the poling direction. Due to the rearrangement of the dipolar molecules, absorption of the polymeric film after poling is less than that of the film before poling. From the absorbance change, the order parameter of the poled film could be estimated, which is related to the poling efficiency. The second-order nonlinear coefficient d₃₃ was taken from the second harmonic generation （SHG） experimental setup. When the concentration of chromophore DCDHF-2-V is 15%, the d₃₃ value is maximum. The relation between the second-order nonlinear coefficients d₃₃ and d₁₃ for the poled polymer film was also discussed in detail. In the same way, another chromophore doped PMMA was investigated.3. The polymer P1 containing tricyanofuran units was synthesized by Friedel-Crafts reaction. Second-order NLO properties of the polymer were measured by SHG. Compared with the polymer （DCDHF-2-V/PMMA）, P1 possesses competitive optical nonlinear stability.4. The non-linear optical films were fabricated by means of alternate electrostatic adsorption with positively charged diazoresin （DR） or with negatively charged azo polymer （PAZO）. Regular film growth during adsorption was proved by means of UV-vis spectroscopy and quartz crystal microbalance （QCM）. Upon the UV irradiation, accompanied with the transition of the ionic bonds between the layers to covalent bonds, the resulting multilayer films possess excellent environmental stability and high thermal stability. The SHG signal can retain 90% when the film is heated up to 200℃.5. The strip waveguide using the DCDHF-2-V/PMMA plolymer film was fabricated by semiconductor technology. The refractive index distribution and mode field distribution of the strip waveguide were simulated. These works give a solid foundation for the final realization of the prototype of polymer waveguide Mach-Zehnder modulator.更多还原