【作者】 周中军；

【导师】 黄旭日； 李志儒；

【作者基本信息】 吉林大学 ， 物理化学， 2011， 博士

【摘要】 在当今迅猛发展的信息时代里,光子材料对光信息处理、光通讯、光计算机的发展,具有重要的战略意义。非线性光学（NLO）材料及其特性的研究是其中的一个重要的领域。也是目前国际前沿课题之一。寻找和设计高性能的非线性光学材料是这一领域发展的重要基础。本文采用精确的从头算（ab initio）和密度泛函理论（DFT）等量子化学方法,对修饰的石墨烯纳米分子以及一些重要小分子体系的非线性光学性质进行了深入的理论研究。主要贡献如下：一、石墨烯纳米带（Graphene Nanoribbon, GNR）作为优秀的共轭桥被引入到推电子基团（Donor）一共轭桥（Conjugated Bridge）一拉电子基团（Acceptor） （D-B-A）模式中来设计高性能非线性光学材料。由于GNR共轭桥自身独特的平面双自由基结构,NH2-GNR-NO2分子展示出了极大的第一超极化率（β0）,其中,NH2-（7,3）ZGNRs-NO2分子的β0值高达2.5×10⁶au（22000×10-30 esu）,这个值是β0实验纪录值（1470×10³0 esu）的15倍。并且发现了二阶非线性光学性质（β0）与石墨烯纳米带尺度的依赖关系：在沿着推拉电子基团的方向上,β0值随着纳米带长度的增加而急剧增加。这里称其为共轭桥的长度效应；在面内垂直于推拉电子基团的方向上,p0值随着纳米带宽度的增加而陡然增加,这里称其为共轭桥的宽度效应。此宽度效应首次被报道。通过比较发现宽度效应优于长度效应。这将丰富以往对共轭有机非线性光学材料的设计与研究。二、以推电子基团-石墨烯纳米带共轭桥一拉电子基团模式为基础来设计更小尺度的非线性光学材料。1)在NH2-GNR-NO2体系中,改变GNR共轭桥的形状但不改变共轭桥的碳原子数。结果发现体系中苯环数越多,其p0值越大。重要的是共轭桥的形状对体系的二阶NLO性质起着关键性的作用。如三角形共轭桥体系（NH2-GNR-NO2）表现出了最好的二阶NLO性质,在CAM-B3LYP/6-31 G*水平下,其β₀值高达1.7×10⁵au。2)在纳米带边缘取代供电子基团如氨基（-NH2）,使体系形成一个面内推拉电子模式。同时在纳米带上方进行锂（Li）掺杂,形成一个面外推拉电子模式。双重推拉电子模式极大的加强了体系的二阶非线性光学性质。上述两种方法都是在不增加体系纳米尺寸的情况下而有效地增大了体系的二阶NLO性质。三、基于从头算方法,我们提出用外加电场这一物理方法来诱导弱相互作用体系（NH3-HCl和H20-HCl）发生质子转移从酸（HCl）到碱（NH3/H20）.研究表明当电场在沿着质子转移方向的场强达到或超过临界电场时,质子转移即可发生。在电场诱导质子发生转移时,体系的二阶非线性光学系数（β0）突然大幅增加。表明电荷转移对体系的二阶非线性光学性质有着重要影响。这项研究为我们日后利用电场来设计高性能非线性光学材料带来了启发。四、在UMP2（Full）/aug-cc-pVTZ水平上,我们研究了取代效应和协同效应对单电子卤键复合物（H3C…C1F）谱学性质和光学性质的影响。当拉电子基团（如F原子）取代甲基中的氢原子时,相互作用能、C1-F蓝移和第一超极化率（β0）全都降低。当推电子基团（如H3C-）取代甲基中的氢原子时,相互作用能、C1-F蓝移和第一超极化率（β0）全都增加。另外,在三体H3C…ClF…ClF体系中,协同效应加强了单电子卤键的强度也增加了第一超极率（β0）。NBO和AIM结果表明电荷转移在卤键强度、谱学及非线性光学性质上起着非常重要的作用。更多还原

【Abstract】 In today’s high-technology world, photonic materials are very important in many fields, such as optical process of information, optical computer, optical communication, etc. The research of the nonlinear optical materials is an important field of its development and is one of the international frontier topics at the present. The searching and designing of high-performance NLO materials is an important base in this field. In this thesis, the structures and nonlinear optical properties of the modified graphene nano-molecules and some important small molecules are investigated by the quantum chemical methods-ab initio and density functional theory (DFT). The main contributions are as followings:1. Graphene nanoribbon (GNR) as an excellent conjugated bridge was used in a donor-conjugated bridge-acceptor (D-B-A) framework to design high performance second-order nonlinear optical materials. Owing to the unique diradical planar conjugated bridge of GNR, (NH2)-GNR-(NO2) exhibits exceptionally large static first hyperpolarizability (β0) up to 2.5×106 a.u. (22000×10-30 esu) for H2N-(7,3)ZGNR-NO2 (ZGNR=zigzagedged GNR), which is about 15 times larger than the recorded value ofβ0 (1470×10-30 esu) for the D-A polyene reported by Blanchard-Desce et al. Interestingly, we have found that the size effect of GNR plays a key role in increasingβ0 for the H2N-GNR-NO2 system, in which the width effect of GNR perpendicular to the D-A direction is superior to the length effect along the D-A direction. It enriches the design and research of conventional organic NLO materials.2. Based on the donor-GNR conjugated bridge-acceptor (D-B-A) framework, we have designed smaller scale and high-performance nonlinear optical (NLO) materials.1) In the NH2-GNR-NO2 system, different shaped conjugated bridges of GNR with the same number of carbon atom are designed. We find that the more the fused bezene ring, the larger theβ0 value. Besides, the shape effect of GNR plays a very important role in enhancingβ0 for NH2-GNR-NO2 systems, such as the NH2- triangle-GNR-NO2 system displays a very largeβ0 value up to 1.7×105 au at the CAM-B3LYP/6-31G*.2) Substituting a donor (-NH2) on the edge of GNR forms one donor-acceptor mode. Meanwhile, Li doping into GNR forms another donor-acceptor mode. The twofold donor-acceptor mode greatly enhances NLO properties but not enlarge the size of systems.3. On the basis of ab initio method, we propose a physical method of external electric field (Eext) to drive the proton transfer from acid (HCl) to base (NH3/H2O). Our results show that when Eext along the proton-transfer direction achieves or exceeds the critical electric field (Ec), the proton transfer occurs. At the same time, theβ0 value of H3N-HCl and H2O-HCl is greatly increased. It is shown that the charge transfer has a key role in enhancing NLO property. This work inspired us to apply the external electric field to design NLO materials for our future work.4. The effects of substitution and cooperativity on spectrum and nonlinear optical properties in H3C…ClF complex has been studied with quantum chemical calculations at the UMP2(Full)/aug-cc-pVTZ level. The electron-withdrawing group (F atom) in the methyl (H3C-) makes the blue shift and the first hyperpolarizability (β0) decrease, whereas the electron-donating group (methyl group) in the methyl (H3C-) causes them increase. The cooperativity between different two types of halogen bonds in H3C…ClF…ClF complex enhances the strength of single-electron halogen bond and hyperpolarizability. The results of AIM and NBO show that the charge transfer plays an important role in enhancing the interaction, spectrum, and nonlinear optical properties.更多还原