【作者】 李凯；

【导师】 张汉壮； 张厚玉；

【作者基本信息】 吉林大学 ， 光学， 2011， 博士

【摘要】 分子聚集体是由相同或不同分子之间,因彼此的弱相互作用而形成的分子体系,这类物质由分子组成,彼此之间不是共价键结合,而是在弱相互作用力作用下规则有序的排布在一起,形成规则的结构。在染料分子材料体系和生物体系中的光合作用中心都有各种形式的聚集体的存在。自Jelly和Scheibe发现分子聚集现象以来,分子聚集体的光谱的研究一直是分子光谱学研究的热点问题。深入理解聚集体光谱行为,如吸收带窄化,超辐射等现象等,对于更好的开发和应用分子聚集体材料显得至关重要。由于分子间的相互作用具有显著的各向异性的特点,分子聚集体会在低维尺度上如一维或二维方向上形成有效的激发。由于聚集体独特的尺度和体系的复杂性,特别是考虑到环境的因素,基于单分子光谱的理论方法往往不能够阐明聚集体中的电子和能量转移的问题,因而发展适用于研究分子聚集体光谱的理论计算方法对于更好的理解和认识聚集体的光谱行为显得尤为重要。在本第一章,我们介绍了分子聚集体的概念,特殊的光学性质以及研究分子聚集体的意义。并且以Jasper组对一维线性直链和圆环及圆柱型分子聚集体的理论研究方法,Spano组对风车型和鱼骨架型分子聚集体包含了电子振动影响的理论研究方法,以及严以京教授基于量子耗散方法研究聚集体激发态弛豫,光谱展宽,激子态动力学以及能量转移领域的方法为例,介绍了目前的理论研究进展。在本章的结尾介绍了本文的研究思路、方法和主要成果。在本文第二章,我们介绍了在理论上研究分子聚集体光学性质所需要的一些基础知识,包括含时哈密顿算符,微扰理论,费米黄金法则,分子聚集体中的吸收光谱以及用时间相关函数描述的吸收谱线。然后我们详细介绍了在这些理论基础以及对前人研究方法的借鉴下,我们建立的新的计算分子聚集体吸收发射光谱的理论方法,我们的方法分为不考虑电子振动的影响的计算方法和考虑电子振动影响的两种计算方法。在本文第三章,我们对低维度分子聚集体的模型进行理论研究,模型分为一维系统和二维系统两大部分。在一维模型中,我们建立了单一的一维线性直链J型分子聚集体模型和H型分子聚集体模型。重点研究分子排列结构和环境热库对分子聚集体性质的影响。这些影响因素包括单分子固有属性,分子聚集体结构参数以及环境热库影响。结合这些影响因素,我们通过分子聚集体的本征值域,态密度分布,振子强度分布,激子占有几率以及离域长度等对聚集体的吸收和发射谱线进行更深入的分析。在二维系统中,我们建立了偶极矩完全平行的双链结构模型和链间偶极矩不平行的鱼骨架型结构模型。二维分子聚集体由于其结构的复杂性,所以结构参数的变化会引起一些独特的光谱变化,如同时存在的J聚集作用与H聚集作用的竞争关系,吸收谱线的分裂(J吸收峰和H吸收峰),两个吸收峰的相对强度随偶极矩角度变化性质等。在本文的第四章,我们计算了喹吖啶酮衍生物N,N-二丁基取代喹吖啶酮(DBQA)晶体的吸收和发射光谱,并且与实验结果进行对比分析。我们选择DBQA作为研究对象是因为它具有优良的发光性质,广泛的应用范围和多晶相特性。我们对DBQA的A晶相和B晶相晶体的吸收和发射光谱进行了计算。在计算和分析过程中,我们将两种晶相结构进行了细致的解析,并列出了其分子聚集体内主要的分子偶极相互作用。结合计算结果与实验的对比,我们指出DBQA晶体荧光谱线中出现的肩峰现象是由电子振动能级作用引起的。更多还原

【Abstract】 Molecular aggregate is the molecular system which is combined by the weak interaction. The component of the system may be the same molecules or different molecules, and the interaction is the non-covalent intermolecular forces. The molecules in aggregate always form an ordination structure by the weak interaction.The aggregates are existed variously in the dye molecular material system and biologic photosynthesis system. The study of the spectrum in molecular aggregate is always the hotspot topice in molecular spectroscopy, since Jelly and Scheibe found the molecular aggregate phenomenon. The deeply understanding of the spectrum behavior of molecular aggregate, for example, the exchange narrowing, super-radiation, e.q., will be of great importance in developing and applying aggregate material. Because the interaction between molecules has the prominent character of anisotropic, the molecular aggregate will form effective excitation in low dimension, for example, one- or two- dimension. Because of the unique size and dimensional complexity in aggregate, especially considering the effect of surrounding environmental, the theoretics based on monomer molecular spectrum are unable to explain the problems of electronic and energy transfer in molecular aggregate. So the development of theoretic calculation methods for the spectroscopy of the aggregate is very important for the understanding and realizing the optical behavior of molecular aggregate.In the first chapter, we introduce the conception of the molecular aggregate, the special optical character and the significance of studying the spectroscopy of molecular aggregate. Then, we introduce the modern theoretical investigation development, for example, J.Knoester’s work based on the calculation about one dimensional straight chain molecular aggregate have extended to the ring aggregate and the cylinders aggregate of helical structure, Spano’s work about the pinwheel and herring-bone aggregate model including the electronical vibration effect, and the prof. Yijing Yan’s work about the studying of relaxation from excited states in aggregate system, the spectrum broadening, the exciton state dynamic and the energy transfer, based on the quantum dissipation theory. Then, we introduce the research methods and achievement in this article by the end of this chapter.In chapter two, we start with the introduction of some necessary fundamentals, including the time-dependent Hamiltonian, perturbation theory, Fermi’s golden rule, absorption spectra of molecular aggregates, and the time-correlation function description of absorption lineshape. Then we describe our calculation method which is created based on these background and other’s work. We could calculate the absorption and emission spectrum of molecular aggregate with or without the influence of electronical vibration.In the third chapter, we theoretically study the low-dimensional model of molecular aggregate (one- and two-dimensional models). In one-dimensional model, we establish the linear straight chain models, they are of pure J- or H-molecular aggregate. The focus of our study is about the influence of molecular arrange structure and the host environment. The influential factors contain the character of isolated molecule, the parameters of aggregate structure, and the influence of host environment. Combined with these factors and eigenvalue area, density of state, oscillator strength, occupation, delocalization and localization, we deeply analyse the absorption and emission spectrum of aggregate. The complexity of two-dimensional structure model leads to some special optical characteristic with the change of structure parameters in aggregate. For example, the competition between J- and H-aggregate effect, the split of absorption spectrum and the variable relative intensity of two absorption peaks.In chapter four, we use our method to calculate the absorption and emission spectrum of the crystal of N,N-di(n-butyl)quinacridone (DBQA), and compare the results with the experiment. We choose DBQA as the subject is because of its good character and wide range of application. The DBQA crystals have many different crystal phases, we calculate the absorption and emission spectrum of phase A and phase B crystals. During the process of calculation and analyse, we parse the structure of the two phases, and list the important couplings between molecular dipole moment in the aggregate. Compare our calculation result with the experiment, we point out that the shoulder peak is due to the electronic vibration effect in the emission spectrum of DBQA crystals.更多还原