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分子双光子吸收特性和聚集效应的理论研究
Theoretical Study on Two-photon Absorption Properties and Aggregation of Molecules
【作者】 李小静;
【导师】 王传奎;
【作者基本信息】 山东师范大学 , 原子与分子物理, 2010, 硕士
【摘要】 20世纪60年代激光器的诞生为非线性光学的迅速发展指明了方向,使之成为现代光学的一个重要分支,并且越来越受到人们的广泛关注。近几十年来,由于非线性光学材料在激光的倍频、混频、参量放大与振荡、集成光学、光学通讯、光束转向、光束畸变消除、图像放大与变换、光信息处理余光信号控制、光受限与阈值监测、全光学连接、光计算机等领域显示出较好的应用前景,探索新型非线性光学材料的研究工作,受到国内外学者广泛关注。与此同时,由于有机分子非线性光学材料具有宽的响应波段、高的光损伤阈值、良好的柔韧性、较低成本以及易于合成、可以进行裁减和修饰等许多无机材料所无法比拟的优点而备受关注。溶剂效应是影响分子非线性光学性质的重要因素。最近,实验及理论工作者发现,极性分子之间的聚集效应对分子双光子吸收性质有重要的影响作用,聚集效应受到人们的广泛关注。本文主要基于从头计算的量子化学方法,利用含时密度泛函理论和响应函数方法,研究了一系列有机分子材料线性和非线性光学性质,讨论了分子几何结构及溶剂中聚集效应与双光子吸收性质之间的关系。本文的研究工作分为两大部分:第一部分研究了最近实验合成的一系列有机分子的单光子和双光子吸收性质;第二部分讨论了溶剂中,聚集效应对一维极化分子双光子吸收性质的影响。下面将简要介绍本论文研究的主要内容和结果。一、气相下,有机分子的单光子和双光子吸收特性。1、以芴为中心的两类有机分子的单光子和双光子吸收特性。在密度泛函理论水平基础上,研究了以芴为中心的两类有机分子的单、双光子吸收性质。首先,在HF水平上优化分子几何结构,其次,利用含时密度泛函理论(DT-DFT)研究分子的单光子吸收性质,并且利用响应函数方法研究了分子的双光子吸收性质。计算结果表明,在低能量范围内,两类分子都具有较好的单光子和双光子吸收强度,分子的光学性质与分子内的电荷转移过程有关。2、以芘为中心的一系列多枝分子的单光子和双光子吸收性质。首先,在HF水平上优化分子的几何结构,优化后的分子显示出较好的平面性;其次,利用含时密度泛函理论(TD-DFT)研究了分子的单光子吸收性质,最后利用响应函数方法计算了分子的双光子吸收性质。二、聚集效应对分子单光子和双光子吸收性质的影响。在实验中,分子非线性光学性质的测量都是在溶剂中进行的,因此,溶质分子处在溶剂中要与周围的分子发生相互作用,对于极性比较强和含有电负性比较强的原子的有机分子之间容易形成氢键,进而通过氢键作用形成超分子,从而影响溶质分子的几何结构和光学性质。研究中,选取一种一维不对称的有机极性分子,首先,设计了它们由于聚集效应形成的二聚物和三聚物的几何结构;然后利用含时密度泛函理论计算单光子吸收性质,最后,利用响应函数方法计算了它们的双光子吸收性质。本论文分为八章。第一章为综述,简单介绍非线性光学现象,并且回顾了非线性光学和双光子吸收分子材料的研究进展。第二章介绍了研究非线性光学特性的量子化学理论方法,包括玻恩-奥本海默近似、Hartree-Fock近似、密度泛函理论。第三章介绍了近年来基于量子化学从头算法而发展起来的几种计算双光子吸收性质的方法包括态求和方法,少态模型方法,有限场方法和响应函数理论方法。第四章介绍了研究分子的非线性光学性质的溶剂效应时所采用的理论模型和方法。第五章研究以芘为中心的两类有机分子双光子吸收性质。第六章研究以芘为中心的一系列多枝分子的非线性光学性质。第七章研究聚集效应对一维不对称极性分子双光子吸收的影响。第八章进行了总结和展望。
【Abstract】 In the 1960s, the birth of laser promotes the rapid development of non-linear optical and makes it to be an important branch of modern optics. Nonlinear optics has more and more attracted people?s attention. In recent years, scientists have shown considerable interest in exploring new nonlinear optical materials, thanks to their widely use and attractive application foreground, such as, laser frequency doubling, laser frequency mixing, parametric amplification and oscillation, integrated optics, optical communication, beam steering, beam distortion removing, image multiplication and transformation, optical limiting and threshold monitoring, complete optical connecting, optical computer and other fields. Meanwhile, much emphasis has been put on organic nonlinear optical materials because they have many advantages that inorganic materials can?t pursue, such as wide response wave band, high optical damage threshold, well flexibility, low cost and easy combination and modification. Solvent effects are important factors to molecular nonlinear optical properties. Recently, experimental and theoretical results have shown that the aggregation effect among the polar molecules has important effect on two-photon absorption properties. Aggregation effect is thus a hot topic in the community.The thesis studies the linear and nonlinear optical properties of various newly synthesized organic molecules utilizing quantum chemical computional methods on the base of the ab initio level. Some structure-property relation is presented and the solvent effect on the geometrical structures and optical properties of the molecules are investigated. The research contains two parts: one is the study of the one- and two-photon absorption (OPA and TPA) properties of a series of newly synthesized organic molecules in gas phase, the other part is related to the aggregation effect on TPA properties of one-dimensional polarized molecules. The main contents and results are described as follows. I. The one- and two-photon absorption properties of organic molecules in gas1. The OPA and TPA properties of two newly synthesized compounds with fluorene asπcentre (noted as SK-G1 and NT-G1) are calculated using response theory at density functional theory (DFT) level. Firstly, we optimize the molecular structures at Hartree-Fock (HF) level. Then, we study OPA properties at DFT level and TPA properties using response functional method. The results show that, in low energy region, molecules have good OPA and TPA intensities, which are related to intramolecular charge transfer process.2. The OPA and TPA properties of a newly synthesized series of pyrene-core derivatives. At first, the molecular geometrical structures are optimized at HF level, and compounds display good coplanarity. The time-dependent density functional theory (TDDFT) is applied to calculate the OPA properties of the compounds. The TPA calculations of the compounds are completed utilizing the response functional theory at DFT level.II. Aggregation effect on OPA and TPA properties of molecules In the experiment, nonlinear optical properties of molecules are measured in solution. Some organic polar molecules that contain stronger electronegativity atoms may have hydrogen bonds among them, which have influence on the structures and optical properties of molecules. The aggregation effect on OPA and TPA properties should be considered.We take one-dimensional asymmetric polar molecules as our research system. Firstly, we design the geometric structures of dimers and trimers formed through aggregation effect, then, TDDFT is applied to calculate the OPA properties. Finally, the TPA properties are studied utilizing the response functional theory at DFT level.The content of this thesis is as follows. There are eight chapters.The first chapter gives a brief introduction of nonlinear optics and also the developing process of the nonlinear optics and nonlinear optical materials. In the second chapter, some quantum chemistry theories of studying the nonlinear properties are introduced, including the Born-Oppenheimer approximation, the Hartree-Fock approximation and the density functional theory. In the third chapter, the different approaches developed recently for calculating molecular two-photon absorption properties are summarized, including sum-over-state, few-state model, finite field and response functional theory methods. The fundamental ways of dealing with the solvent environment are discussed in the forth chapter. In the fifth chapter, we discuss two-photon absorption properties of two kinds of compounds with fluorene as centre. One-photon and two-photon absorption properties of a series of pyrene-core derivatives are studied in the sixth chapte.In the seventh chapter, aggregation effect on two-photon absorption properties of the asymmetric polar molecules are studied. The summary and prospect are presented in the last chapter.
【Key words】 One-photon absorption; Two-photon absorption; Aggregation effect; Charge transfer; Organic molecule;