【作者】 赵亮；

【导师】 苏忠民；

【作者基本信息】 东北师范大学 ， 物理化学， 2009， 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。本论文利用密度泛函和半经验AM1、ZINDO等量子化学方法对系列rubrene和开孔富勒烯等新型π共轭体系的结构和非线性光学性质进行详细的理论讨论,主要内容包括以下五个方面:1.通过对红荧烯（rubrene）双光子吸收性质的理论研究,发现红荧烯相对于并四苯的双光子吸收截面值大得多,证实了存在着从悬挂的苯基到并四苯分子骨架间的对称电荷转移。故此引入对称性的电荷转移也是一个非常有效的增加双光子吸收截面的途径。此外,通过增加红荧烯的共轭范围,双光子截面增加明显。然而在红荧烯的悬挂苯基上引入电子的给体氨基或者电子受体硝基,均会使双光子吸收截面显著下降。所以从双光子吸收分子设计角度来说,增加有效π共轭范围是得到具有大的双光子吸收截面分子的最好选择。2.通过对一系列以硼为中心多分支低聚芴的双光子吸收性质理论研究,发现增加分支数目能够显著增加低聚芴的双光子吸收截面值。相对于双分支和单支低聚芴,三分支低聚芴CBTFn的双光子吸收截面值最大。采用简化激子模型来讨论CBTFn的双光子吸收截面值,说明在硼原子中心和芴分支间存在很强的有效电子耦合作用。此外存在于三分支CBTFn中的耦合作用要比双分支CBDFn中的耦合作用要强,这表明当分支与中心间的耦合允许时,三分支分子比双分支分子是更好的具有大的双光子吸收截面的选择。3.通过对在通常的有溶剂中就能很容易溶解的PPV衍生物poly [2-（9-phenylanthracen-10-yl）-1, 4-phenylenevinylene] （P1）的双光子吸收性质的理论研究,发现相对于PPV,由于在P1中引入悬挂基团,P1的双光子吸收截面值明显下降。这主要是由于悬挂基团大大减少了分子本身的有效共轭范围。P1的最大双光子吸收截面所对应电荷转移发生在PPV主链与悬挂基团之间,故此苯基蒽悬挂基团被认为是很好的双光子受体。从应用的角度来看,我们通过在PPV上引入某些基团使得PPV易于被加工,另一方面,应该尽可能保持PPV主链的π-共轭伸展。这两方面应该作为设计具有应用前景双光子吸收材料基本原则。4.通过对一系列富勒烯C₆₀开孔含氧衍生物的结构、稳定性和非线性光学性质理论研究,发现相对于C₆₀,五元开孔含氧衍生物C₅₅O₅的HOMO-LUMO带隙比C₆₀的HOMO-LUMO带隙高,说明C₅₅O₅具有较高的化学稳定性。结合能计算表明五元开孔含氧衍生物C₅₅O₅要比六元开孔含氧衍生物C₅₄O₆更容易形成,我们预测C₅₅O₅的实验合成一定能够实现。由于开孔含氧富勒烯C₆₀衍生物破坏了C₆₀的对称中心,具有相对较大的二阶非线性光学响应,这一发现对于寻找基于C₆₀的新型非线性光学材料开拓了一个新的方向。对于C₅₅O₅与C₅₄O₆的二阶非线性光学响应的主要贡献分析表明沿Z轴的电荷转移是最重要的。5.通过对一系列富勒烯C₅₀开孔含氧衍生物的结构、稳定性和非线性光学性质理论研究,发现相对于D5h C₅₀,将其五元开孔含氧衍生物用氟饱和5/5键C₂位置所形成C₄₅O₅F₁₀(C_5V)的HOMO-LUMO带隙高于相同水平下C₆₀的HOMO-LUMO带隙,说明C₄₅O₅F₁₀具有较高的化学稳定性。结合能计算表明C₄₅O₅F₁₀相对于D5h C₅₀其他打开一个完整五元环或六元环形成的含氧衍生物（包括开孔后用卤素饱和5/5键C2位置所形成衍生物）更容易形成。表明C₄₅O₅F₁₀(C_5V)的实验合成是可能的。对C₄₅O₅F₁₀(C_5V)的二次谐波产生下动态一阶超极化率计算表明:C₄₅O₅F₁₀在从0到1.5 eV间很宽的范围内色散很小,这表明C₄₅O₅F₁₀在频率转换光学材料领域有着潜在的应用前景。对于C₄₅O₅F₁₀的二阶非线性光学响应的主要贡献分析表明沿Z轴（C₅）的电荷转移是最重要的。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 （NLO） field, due to their large nonlinear optical coefficient, fast nonlinear optical response times, relatively low cost, ease of fabrication and integration into devices, tailor ability which allows one to fine tune the chemical structure and properties for a given nonlinear optical process, high laser damage thresholds. In this thesis, in order to design and select organic materials with large two-photon absorption response, we have performed systematic theoretical research of novelπ-conjugated materials. The quantum chemical methods-density functional theory and AM1 have been applied to obtain the molecular equilibrium geometries. On the basis of the optimized molecular geometries, one- and two-photon absorption properties are obtained by ZINDO-SOS method. In addition, we also performed systematic investigations on the structure, stability and NLO properties of open-cage C₆₀ and C₅₀ derivatives. These results may provide a theoretical basis of designing novel fullerene derivatives with large NLO coefficients. Our work has been focus on the following five aspects:1. One- and two-photon absorption properties of a noteworthy perpendicularπ-electron system rubrene have been investigated. Calculation results show that relatively larger two-photon cross sections (δ_max) of rubrene than that of tetracene verify that there exits CT from phenyl groups to the tetracene backbone. So introducing symmetrical CT is also one of effective ways to enlarge theδ_max. By enlarging theπ-conjugation extension of rubrene, theδ_max show a distinct increase, However, attaching electron donating amino group or electron withdrawing nitro group to rubrene bring apparent decrease ofδ_max in contrast with rubrene. So from the molecular designing aspect, the extension ofπ-conjugation is the best choice for relatively largerδ_max.2. One- and two-photon absorption properties of a series of three-branched and two-branched as well as one-branched oligofluorenes with boron center have been theoretically investigated. Changing the number of branch brings significant enhancement on theδ_max values. CBTFn has the largestδ_max with respect to CBDFn and CBSFn. The comparisons ofδ_max with simplified exciton model show that the effective coupling between boron center and individual fluorene arm is relatively strong. Moreover, the coupling in CBTFn is larger than that in CBDFn, which also proves that the three-branched ologomer is a better choice for attaining largerδ_max than the two-branched counterpart when the coupling between the center and the individual arm is allowed. So CBTFn is a kind of promising TPA materials for optical power limiting. 3. One- and two-photon absorption properties of a novel PPV derivative poly 2-（9-phenylanthracen-10-yl）-1,4-phenylenevinylene （P1）, which are highly soluble in common organic solvents, have been investigated. The pendent groups bring a significant decrease on theδmax value of P1 compared with PPV. This decrease can be explained by the influence from pendent groups on the effectiveπ-conjugation length of P1. In addition, the charge transfer contributing to TPA of P1 is through backbone to pendent group, so the pendent group of P1 can be regarded as a good two-photon absorber. From the application point of view, on one hand, it should introduce certain group to make PPV easy fabrication. On the other hand, it should keep goodπ-conjugation extension of PPV backbone. In general, for a promising TPA materials for application, the above two aspects should be taken into consideration.4. The structural and electronic as well as NLO properties of a series of open-cage oxo fullerene C₆₀ derivatives: C₅₅O₅ and C₅₄O₆ have been theoretically investigated. Calculation results indicate that C₅₅O₅ is a chemically stable structure with a larger band gap compared to C₆₀ calculated at the same theory level. The cohesive energy calculations reveal that the formation of C₅₅O₅ may be easier than that of C₅₄O₆, which may provide useful guidance for experiments. Therefore, it makes us to believe that the experimental synthesis of C₅₅O₅ will certainly be able to achieve in the near future. When the cage of C₆₀ is opened, it induces relatively larger second-order NLO response, thus it opens a novel route towards the research on searching new type of NLO materials based on C₆₀ derivatives. Analysis of the main contributions to the second-order NLO response of C₅₅O₅ and C₅₄O₆ reveals that charge transfer along the z-axis direction plays a key role.5. The structural and electronic properties as well as NLO properties of a series of open-cage oxo D5h C₅₀ derivatives: C45O5 and C44O6 have been theoretically investigated. Calculation results indicate that C₄₅O₅F₁₀, which is from D5h C₅₀ open-cage oxo derivative C45O5 and then saturated with ten fluorine atoms at pentagon-pentagon vertex fusions, is a chemically stable structure with a larger band gap compared to C₆₀ calculated at the same theory level. The cohesive energy calculations reveal that the formation of C₄₅O₅F₁₀ may be easier than the open-cage oxo D5h C₅₀ derivatives: C45O5 and C44O6 （including their corresponding halogen passivated derivatives）. Therefore, it makes us to believe that the experimental synthesis of C₄₅O₅F₁₀ will certainly be able to achieve in the near future. The dynamic second-order NLO response of C₄₅O₅F₁₀ shows small dispersion behavior in a wide frequency range from 0 to 1.5 eV under second harmonic generation （SHG） process, showing that C₄₅O₅F₁₀ is available to be used for frequency conversion optical materials. Analysis of the main contributions to the second-order NLO response of C₄₅O₅F₁₀ reveals that charge transfer along the z-axis direction plays a key role.更多还原