【作者】 杨国春；

【导师】 苏忠民；

【作者基本信息】 东北师范大学 ， 物理化学， 2007， 博士

【摘要】 随着现代光通讯、光计算和光信号处理等领域的高速发展,越来越需要一些具有大的非线性光学系数的材料作为光子器件的基础。有机π电子共轭体系具有较大的非线性光学系数、响应速度快、成本低、容易加工、结构可调性好、高的损伤阈值,因此受到了人们广泛的关注。另一方面,理论计算可以直接获得非线性光学系数张量的各个分量,不像光学实验得到的只是一个宏观量,从而成为研究分子性质的有效工具。由于分子间的相互作用或集体效应,通常一个宏观量不能直接转换成微观量,因此,计算分子的非线性光学系数并与实验值进行比较,对建立结构和性质之间的关系以及理解这些效应对分子光学非线性响应影响的程度意义重大。本论文利用密度泛函理论结合完全态求和方法研究了系列新型有机非线性光学材料。通过理论计算详细地给出并五苯-金异构体、酚基吡啶硼配合物、有机胺六钼酸盐衍生物、螺旋硅双芴体系的几何结构、电子光谱、电荷传输机理和非线性光学性质等信息,这为结构—非线性光学性质间关系的建立奠定了基础,并且为实验提供了有价值的理论依据,为进一步探索具有较大的非线性光学系数的有机材料奠定了基础。研究工作主要包括以下五部分。1.用时间相关密度泛函理论结合完全态求和方法(TDDFT-SOS)计算系列有机小分子体系的非线性光学系数,与文献报道的理论值和实验值相比较,结果显示TDDFT-SOS方法计算的非线性光学系数与实验值得到较好的符合,并与CCSD(T)方法计算精确度相当,表明用此方法研究有机体系的非线性光学性质是可行的。同时研究12种不同泛函对TDDFT-SOS方法的影响,并从计算结果的精确度和计算效率方面进行了系统分析。2.用密度泛函理论研究了并五苯-金异构体的结构、电子光谱和二阶非线性光学性质。结果表明,当一个金原子加到并五苯上时,金原子与并五苯中心苯环上的碳原子相连的体系最稳定,其中金原子与碳原子形成共价σ单键,但是其它体系中金原子与碳原子存在强的给受体相互作用。此外,苯环的数目对金原子与碳原子之间的成键性质和相互作用影响较大,增加苯环的数目能够缩短Au—C键的距离和增加Au—C键的强度。但是当苯环的数目是9个时,Au—C键距离不再改变。当两个金原子加到并五苯也能缩短Au—C键的距离,并且两个金原子在并五苯异侧时形成的异构体更稳定。金原子加到并五苯上时,明显地改变了并五苯的跃迁方式,增加了可能的电子跃迁。这些异构体具有可应用的二阶非线性光学系数,分析表明从金原子到并五苯的电荷转移对非线性光学响应起主要贡献,体系4的二阶非线性光学系数是体系1的近四倍,这说明微小的结构调整,能够明显地提高非线性光学响应。3.用密度泛涵理论优化了可以作为单层器件的酚基吡啶硼配合物阴离子、阳离子和中性分子几何构型,在此基础上计算了吸收和发射光谱。其吸收和发射光谱主要是由三苯胺到酚基吡啶的电荷转移组成。从重组能角度看,空穴迁移率大于电子迁移率,然而电子的交换积分大于空穴的交换积分,综合这两个因素,电子和空穴的迁移率几乎相当,这从理论上解释了其可以做成单分子发光器件的原因。结合前线分子轨道和阴离子、阳离子的几何结构变化,三苯胺起到传输电子,酚基吡啶起到传输空穴的作用。鉴于其具有较大的二阶非线性光学系数、高的透明性和稳定性等优点,该体系有望成为较好的二阶非线性光学材料。4.用密度泛函理论方法研究六钼酸盐有机胺衍生物的电子光谱和三阶非线性光学性质,得出如下主要结论。有机胺部分作为电子给体,多阴离子作为电子受体,形成给体-受体-给体电荷转移模型。结果表明GRAC势是计算此类体系电子光谱的有效方法,六钼酸盐有机胺衍生物与六钼酸盐相比,有机胺加到六钼酸盐上增加了从基态跃迁到激发态的几率,有机胺的对位取代和直角位取代具有不同的跃迁性质。六钼酸盐有机胺衍生物具有较大的三阶非线性光学系数,有机胺到多阴离子的电荷转移对有机胺六钼酸盐衍生物的非线性光学性质起决定作用,增加π共轭长度是提高此类体系非线性光学响应的有效途径。5.用密度泛涵理论研究螺旋硅共轭结构体系的二阶非线性光学系数,结果表明用氮原子取代碳原子有利于提高体系的非线性光学响应,此类体系具有许多有利于作为二阶非线性光学材料的优点。与典型的尿素分子相比,该体系具有较大的二阶非线性光学系数。此类体系在较大的宽频区表现出较小的色散行为,它们可以用于频率转换材料。此类体系小的偶极矩能够保证此类材料具有较大的宏观二阶极化率。此类体系在可见光区具有较好的透明性,能够满足非线性光学材料对透明性的需求。更多还原

【Abstract】 With the rapid development of optical telecommunication, optical computing and signal-processing devices etc, materials with larger nonlinear optical coefficient are still in great demand due to the critical role that they are playing in photoelectric devices. The organic materials are of major interest in the nonlinear optical field, due to their large nonlinear optical coefficient, fast nonlinear optical response times, relatively low cost, ease of fabrication and integration into devices, tailorability which allows one to fine tune the chemical structure and properties for a given nonlinear optical process, high laser damage thresholds. Theoretical calculation can be a good tool for obtaining some insight into molecular property, each tensor component of hyperpolarizability can be assessed directly, unlike optical experiment in which the property is obtained as macroscopic quantity. Usually, a macroscopic quantity cannot be directly converted to a microscopic one due to intermolecular or collective effects. Therefore, calculation of molecular hyperpolarizabilities and comparison of the results with corresponding experimental results are of importance in establishing the structure-property relationship and estimating the amount of such effects on molecular optical nonlinearity.In this thesis, we have performed systematic theoretical research of novel organic nonlinear optical materials by using time-dependent density-functional theory combined with sum-over-states method （TDDFT-SOS）. Gold-pentacene complex, phenolpyridyl boron complexes, organoimide derivatives of hexamolybdates and spirosilabifluorene derivatives were optimized by density functional theory. On the basis of the optimized molecular geometries, electronic spectrum, charge transport and nonlinear optical properties of these systems are obtained and structure-property relationships are also established. These results may provide a theoretical basis of designing novel materials with large nonlinear optical coefficeents. Our work has been focus on the following five aspects:1. The nonlinear optical properties of a series of organic molecules are calculated by using TDDFT-SOS method and compared with the literature theoretical and experimental values. The results show that our theoretical values are in agreement with the experimental and CCSD（T） ones. This indicates we can use TDDFT-SOS method to study the NLO properties of the organic systems. The effects of different functional/basis set on NLO properties were tested. Moreover, the convergent behaviors and efficiency of various functionals are also discussed.2. Four isomers formed by a gold atom attached to a pentacene molecule were investigated by density functional theory due to their potential applications in molecular electronics. When attaching a gold atom to a pentacene molecule, the gold atom attached to the center benzene ring is the most stable. The gold and carbon atoms can form a covalent bond, which hasσsingle-bond character. However, there are strong donor-acceptor interactions between the gold and carbon atoms of systems 3 and 4. Moreover, the influence of the number of benzene rings on the bonding nature or interactions is great. Increasing the number of benzene rings can shorten the Au-C distance and enhance the Au-C bond strength. However, when the number of benzene rings is 9, the Au-C distance does not change. Adding a gold atom to the pentacene obviously changes the transition nature of pentacene and results in the increase of possible transitions. These systems possess moderate molecular second-order polarizabilities compared with the organometallic and organic complexes. Theβvalue of system 4 is much larger than that of system 1. Thus, subtle variations in the molecular architecture result in substantial enhancement to the second-order NLO response.3. The natural, cation and anion structures of 1,6-bis（2-hydroxyphenol）pyridylboron bis（4-n-butylphenyl）phenyleneamine were optimized with the B3LYP functional. The charge transport properties were investigated within the framework of the charge hopping model. The results show that 1,6-bis（2-hydroxyphenyl）pyridineboron （（dppy）BF） functions acts as a electron transport group and triphenylamine as a hole transport group; the charge transport ability for the two types of carriers is not only high but also nearly balanced, which explains why it is an efficient single-layer electroluminescent device. On the basis of the large second-order polarizability value and high transparency, this compound has the possibility to be an excellent second-order nonlinear optical material. The main origin of this large second-order nonlinear optical response is charge transfer from the triphenylamine group to （dppy）BF.4. Electronic spectrum of organoimide derivatives of hexamolybdates have first been calculated within the time-dependent density-functional theory. The results show that organoimide acts as donor and hexamolybdates as acceptor. Those derivatives possess donor-acceptor-donor （D-A-D） configurations. The accurate electronic absorption spectrum of organoimide derivatives of hexamolybdates can be achieved using the GRAC potential. Adding the organoimide to [Mo₆O₁₉]^2- can increase the transition probability compared to [Mo₆O₁₉]^2-. The transition nature of the diagonal-substituted derivatives is different from that of the orthogonal-substituted derivatives. The organoimide derivatives of hexamolybdates are found to possess remarkably larger static third-order polarizabilities. For our studied systems, increasing the conjugation length and diagonal substituted are efficient ways to enhance the third-order polarizability.5. We have investigated the electronic structure and the second-order nonlinear optics properties of the asymmetric spirosilabifluorene derivatives and elucidated structure-property relationships from the micromechanism. The results show that these compounds possess many favorable features for application in the second-order nonlinear optical field. First, these compounds have remarkably larger molecular second-order polarizabilities compared with the typical organic compounds. Second, all the compounds generate large nonresonant optical nonlinearities over a wide frequency zone, which can be used for a frequency conversion optical material. Third, a small dipole moment can guarantee manifestation of the large macroscopic second-order susceptibility. Fourth, they have high transparency in the visible light area.更多还原