【作者】 汤安民；

【导师】 应晓；

【作者基本信息】 华南理工大学 ， 材料物理与化学， 2010， 硕士

【摘要】 近年来,随着光通讯、光电子学和光信息处理等实用领域的飞速发展,非线性光学(NLO)效应的作用也越来越重要。而由于无机非线性光学材料在其性质上的一些局限,使得人们把注意力逐渐转移到有机材料方面。与无机非线性光学材料相比较,有机非线性光学材料具有易于化学修饰加工、极短的光学响应时间和高的化学损伤阀值等优点,具有广泛的应用前景。如何提高有机生色团的非线性光学性能是这一领域的关键课题之一。在众多的NLO生色团中,卟啉类化合物由于其共轭结构的可控性,表现出优良的非线性光学性能,且利用手性分子本征的非中心对称结构,使其在二阶NLO材料设计方面有着独特的优越性。本论文设计了一系列手性联萘桥联双卟啉分子,通过改变推拉基团的位置,利用激子耦合理论研究其二阶非线性光学性质和空间结构的关系。本文采用密度泛函理论(DFT)B3LYP/6-31G(d,p)方法对所有模型分子进行几何构型优化,用ZINDO方法计算电子光谱,得到基态和各激发态的偶极距;基态到激发态及各激发态之间的跃迁点偶极矩,并得到基态到各激发态的跃迁能、相应的振子强度等参量。运用自编全态求和(SOS)程序计算分子二阶非线性光学系数,得到分子一阶超极化率β矢量在偶极矩μ方向上的投影值βμ、分子一阶超极化率的超瑞利散射值βHRS。本文还利用Hyperchem软件和有限场拟合的方法,分别计算了Ib子的△μ值,从理论上说明使用两种方法计算分子非线性光学系数的可行性。本文从量子力学和量子化学的角度,全面介绍了激子耦合理论及其在二聚体系分子中的应用,并将其应用到不同构型的二聚体系模型分子当中。研究结果表明,卟啉二聚体分子中两个单体卟啉之间有强的激子耦合作用,B带的Davydov分裂大小与两个卟啉环的相对取向以及两卟啉环中心之间距离有关。双卟啉分子中一阶超极化率的大小不仅与推拉电子基团的空间排列方式有关,而且随着单体卟啉非线性性能的增加而增加。联萘桥联具有大一阶超极化率的取代卟啉单体而形成的双卟啉分子IIc的一阶超极化率显著提高,比IIb系列分子提高了近一个数量级。IIc系列分子的一阶超极化率随着推拉基团的排列方式变化规律与IIb系列分子相同,它们都可以用激子耦合的偶极取向模型进行解释。乙炔基的引入使得IIc双卟啉系列分子单体卟啉环中心之间的距离比IIb系列减小,且随着单体卟啉间距离接近,在B带激子跃迁态附近,IIc2系列分子还出现两个邻近卟啉环之间的电荷转移跃迁态(CT态)。三能级模型下跃迁通道分析表明,三能级偶极耦合增强不仅与B带激子跃迁态有关,还与CT态密切相关。研究表明,通过优化双卟啉二聚体分子偶极取向和偶极耦合增强的效应可以提高二阶非线性光学性能。更多还原

【Abstract】 For the past few years, with the development of photo-communication, photoelectronics and optical information processing. Non Linear Optics (NLO) become more and more important. And because of some disadvantages of inorganic NLO, more and nore people Divert their attention to organic NLO. Compared with the inorganic NLO matertial, organic NLO material can be modified and processed easily, fast response time, and high damage threshold. It has comprehensive application foreground and spread value. How to improve the NLO of organic chromophore is the most important thing. Among the NLO chromophores, because of the conjugate structure’s adaptable, porphyrin have excellent NLO property. With natural noncentrosymmetrical structure and intrinsical thermostability, chiral molecules have many unique advantages for NLO materials.In this paper, we studied the second-order NLO properties of some porphyrins, especially the chiral bis-porphyrins. By changing the position of Donor and Accepter electron groups, and using the exciton coupled theory to study the relationship between the second NLO properity and spatial structure. Quantum chemical software Gaussian 03 was employed in calculation, and structures of all molecules were optimized based on the methods of semiempirical B3LYP(DFT) at 6-31G(d,p) basis set level, after which the electronic spectra were calculated by the method of ZINDO. The transition electric dipole moments between ground and excited states, between excited and excited states, the transition energies, the corresponding oscillator strength. Using the SOS program, we calculate the second NLO coefficient, calculated the first hyperpolarizabilitiesβof a series of molecules ,βμ,βHRS, and so on. Finally, we calculated the△μof 1b molecule using the Hyperchem and finite field method, and both of this two methods is correct.Results showed that there were strong exciton coupling interactions between two porphyrin chromophores in these bis-porphyrins, and the Davydov splitting of B bands were related to both distances and relative orientations between two porphyrin rings. The first hyperpolarizabilities of chiral bis-porphyrins depend on the spacial arrangement of the substituents. The increasement of first hyperpolarizabilities in bis-porphyrins is not just related to the increasing of transition dipole moment changes between excited and ground state, but related to the relative orientations between ground state dipole moment vectors and exciton coupling dipole moment vectors as well. For the binaphthyl bridged bis-porphyrins, the second-order nonlinear optical properties could be greatly improved by introducing push-pull substituents on porphyrin chromophore, and it’s more than an order of IIb series molecules. the first-order hyperpolarizability of IIc molecules have the same evolution of IIb series molecules. Which can be explained by the excition model. The introduction of acetylene-based made the distance between the monomer porphyrin ring centers decreased, And with the distance between the two neighboring porphyrin ring decreased, appeared a charge transfer transition state (CT state) between the two neighboring porphyrin ring of IIc2 molecule. Transition three-level model channel analysis showed that three-level dipole coupled with enhanced not only with the B exciton transition state, but also closely related with the CT state. It can be improving second-order nonlinear optical properties by optimization of porphyrin dimer dipole orientation and dipole coupling effect.更多还原