体系相互作用与发光和催化机理研究

发布时间：2018-06-08 23:37

本文选题：相互作用 + 聚合物发光　；参考：《中国科学技术大学》2017年博士论文

【摘要】：材料是支撑人类文明发展的物质基础。高效、经济和实用的新型材料的持续涌现为社会进步提供了不竭助力。因此,新材料的研发成为了当前一项长久的目标。然而,材料结构的复杂性为实验的合成和表征带来了困难。幸运的是,理论计算和模拟从内部机制和电子结构层次为材料的解析提供了有力的工具。特别是近年来高性能计算和复杂电子结构理论和模型的快速发展,使得第一性原理电子结构计算和分子动力学模拟能力进一步提升。从原子和分子尺度上对材料性能进行预测和解释,抓住体系的关键要素,进行合理的构效和设计,与实验相辅相成,成为了新型材料研发的有力手段。不同体系如分子或材料之间的相互作用是连接物质结构和性质的关键桥梁。通过解析体系中分子或材料本身的结构和性能,利用分子间和材料间的相互作用进行理性的构效和复合,为提高材料本身固有性能,弥补缺陷,协同增效,设计并获得新型性能的功能化材料研发提供了新的思路和途径。本论文从不同体系间(分子和材料)的相互作用出发,采用第一性原理的密度泛函理论(DFT)进行模拟计算,研究分子间的相互作用(π-π耦合)对分子发光的影响(第三章)和功函数、电负性等不同的材料间相互作用引起的电荷极化对催化机理的影响(第四章)。主要包括四个部分:第一部分即第一章,主要基于后面的工作介绍了两个内容,第一个是聚合物发光材料研究进展。与改变发光材料本身的内部结构(如官能团修饰,增加共轭长度)调控发光过程相比,通过分子间π-π耦合相互作用形成的聚合物发光材料操作性更大,应用范围更广,因而,引起了人们的关注和研究。虽然最基本的发光原理与其他发光分子相同,但由于分子间的相互作用,聚合物发光又有其独特的内部机制,这种独特的机制为聚合物的发光带来了特定的性能,也为调控分子发光过程提供了可能性。第二个是金属半导体及二维材料催化反应的研究进展。催化反应的核心内容是催化剂的设计和研究。金属催化剂反应性能优越,但缺点是稳定性较差,价格昂贵,而相对而言,半导体催化剂稳定性较好,但催化活性又相对较低。因此,催化剂构效时,可以利用不同材料间的相互作用进行复合,在性能互补的前提下,产生协同效应,提高材料的催化反应效率和稳定性,降低成本。另一方面,作为一类无金属的材料,以石墨烯为代表的二维材料催化剂因其优良的化学稳定性、半导体性、易调控性和优异的光学性质也在化学反应中展现出优越的性能,成为了当前催化研究的一个重要的焦点。第二章主要介绍了以第一性原理为基础的密度泛函理论,包括它的理论框架,发展流程,含时密度泛函理论以及量化应用软件包。密度泛函(DFT)的理论基础是量子力学,其基本研究量是体系的电子密度。通过对Kohn-Sham方程的求解,把相互作用的多粒子体系转换成无相互作用的单粒子体系,并通过合适的交换关联泛函进行近似,经过一系列的循环迭代直到收敛,计算出体系基态时的能量和密度。而在密度泛函中引入含时微扰的含时密度泛函理论,则可更为精确的模拟激发态的电子结构。密度泛函理论在应用上的最终实现依赖量化软件包的计算模拟。第三章介绍了分子间相互作用与分子发光的研究,主要包括两个工作:第一工作是分子聚集诱导系间窜越增强磷光。分子内的系间窜越(ISC)在各种光电应用中起着重要的作用。然而,利用传统的化学修饰和重金属掺杂等方法提高系间窜越几率十分不便,限制了其应用范围。在我们的工作中,我们提出了一种新型的"聚集诱导系间窜越"(AI-ISC)机制。在聚合物分子中,利用分子间相互作用引起的激发态能级分裂,可以改善单重和三重激发态的能级匹配,进而提高系间窜越的几率。通过第一性原理的模拟计算和实验光谱检测,分子聚集体中这种增强的系间窜越几率大大促进了分子的磷光发射。同时,磷光发射也随着聚集程度的增强而发生红移,为磷光波长的调节提供了一个便捷的渠道。第二个工作是自组装有机量子点的发光机制。在这个工作中,我们模拟设计并合成了一种新型的有机染料量子点,该量子点体系在溶液中展现出了超高的荧光量子产率,而其通过疏水相互作用和π-π堆积形成固态时,荧光产率较低,且发光波长对激发波长具有很强的依赖。理论计算发现这种量子点的发光原理为在在溶液中分子聚合被破坏,主要以单分子形式存在,通过与溶剂发生作用,形成了 push-pull电荷转移机制,进而影响了发光效率。而在固态时,分子发生π-π堆积和H-聚集,能级产生分裂,分子振动受到抑制,弛豫变慢,违反了 Kasha's规则,发光波长对激发波长具有很强的依赖性,同时激发态的辐射跃迁几率下降,荧光量子产率降低。第四章介绍了材料间相互作用引起的电荷极化与催化机理的研究,主要包括三个工作:第一个工作是石墨烯基复合材光催化制氢与安全储氢。在这个工作中,我们设计了一种C_xN_y和石墨烯基材料复合的三明治结构,其中,碳氮材料(g-C_xN_y)夹在两层官能团修饰的石墨烯中(GR_F)。第一性原理计算发现,由于g-C_xN_y和GR_F之间相互作用引起的电荷极化,使得这种三明治体系可以同时捕获紫外光和可见光,进而激发产生空穴迁移到外层的GR_F上。在光生空穴的帮助下,吸附在GR_F上的水发生裂解,产生质子,受聚集负电荷的C_xN_y静电吸引,质子穿透石墨烯迁移到C_xN_y上,并在光生电子的作用下,产生氢气。由于外层的石墨烯结构不允许氢气的穿透,使得氢气与外界分离,储存在体系中。综合可知,我们设计的这种三明治复合体系实现了光催化制氢和安全储氢一体化。第二个工作是氮掺杂石墨烯催化还原对羟基苯酚。实验中,通过多种MOF材料为前驱模板在高温下烧结得到了氮掺杂石墨烯的多层碳材料并催化还原对硝基苯酚。含有吡咯N掺杂石墨烯最多的材料催化活性最佳。理论计算通过对三种N掺杂石墨烯的构型,电子结构,吸附性能,导电性的研究,发现:掺杂的N原子和石墨烯由于电负性的差异,相互作用后发生电荷极化,电荷发生聚集,提供活性位点;吡咯N掺杂石墨烯中活性位点附近正电荷聚集最多,对4-NP-的吸附能最强,耦合活化程度较高;吡咯N掺杂石墨烯体系延续了石墨烯材料优良的导电性能,为还原反应的发生提供源源不断的驱动力。因此,吡咯N掺杂石墨烯对催化还原对硝基苯酚具有较高的反应活性,与实验结果吻合。第三个工作是TiO_2-Pd@Pt光催化裂解水。理论和实验合作设计并合成了原子厚度可调节的Pd@Pt壳层结构,并将这种壳层结构与n型半导体,锐钛矿TiO_2结合。在这一体系中,Pd@Pt壳层结构在光催化水裂解反应中,起到了双重功效,这双重功效均取决于复合材料中金属Pt的原子厚度。这双重功效分别是:利用Pd,Pt间相互作用引起的界面电荷极化提高金属上的电子捕获能力,进而促进电荷分离;通过Pt表面电荷密度的增加和晶格应力提高对于水的吸附能力。这些性能的提高显著的增强了光催化裂解水的催化活性。
[Abstract]:Material is the material foundation to support the development of human civilization. The continuous emergence of new materials with high efficiency, economy and practicality has provided an inexhaustible contribution to social progress. Therefore, the development of new materials has become a permanent goal. However, the complexity of the material structure has brought difficulties to the synthesis and characterization of the experiment. Fortunately, theoretical calculation. And simulation provides a powerful tool for the analysis of materials from the internal mechanism and the electronic structure level. Especially in recent years, the high performance calculation and the rapid development of complex electronic structure theory and model make the ability of the electronic structure calculation and molecular dynamics simulation of the first principle to be further improved. From the atomic and molecular scales to material properties The key elements of the system can be predicted and explained, and the key elements of the system are seized and the structure efficiency and design are reasonable. It is complementary to the experiment. It has become a powerful tool for the research and development of new materials. The interaction between different systems, such as molecules or materials, is a key bridge to connect the structure and nature of material. And properties, using the interaction of intermolecular and material to make rational structure effect and compound, and provide new ideas and ways to improve the intrinsic properties of the material, make up the defects, synergy the efficiency, design and obtain the new functional functional materials. This paper is based on the interaction of different systems (molecules and materials). The density functional theory (DFT) of the first principle is used to simulate the effects of intermolecular interaction (PI - pi coupling) on molecular luminescence (third chapter) and the effect of charge polarization on the catalytic mechanism caused by the interaction of power functions, electronegativity and other intermaterial interactions (fourth chapter). The first part is the first chapter, the first chapter Two contents are introduced mainly based on the later work. The first is the progress in the research of polymer luminescent materials. Compared with the changes in the internal structure of the luminescent materials, such as the functional group modification and the increase of the conjugate length, the polymer luminescent materials formed by the interaction of the intermolecular pion coupling interaction are more operable and applied. More widely, it has attracted people's attention and research. Although the most basic principle of luminescence is the same as other luminescent molecules, because of the interaction between molecules, the luminescence of polymer has its unique internal mechanism. This unique mechanism provides specific properties for the luminescence of polymers and provides the possibility for the regulation of molecular luminescence. The second is the progress in the catalytic reaction of metal semiconductors and two-dimensional materials. The core content of the catalytic reaction is the design and research of the catalyst. The catalytic performance of the metal catalyst is superior, but the disadvantage is that the stability is poor and the price is expensive, and the stability of the catalyst is better, but the catalytic activity is relatively low. Therefore, the catalytic activity is relatively low. When the agent is constructed, it can be combined with the interaction of different materials to produce synergistic effects on the premise of complementing performance, to improve the efficiency and stability of the catalytic reaction and to reduce the cost. On the other hand, as a kind of non metal material, the two-dimensional material catalyst with graphene as the substitute for its excellent chemical stability. Semiconductors, easy regulation and excellent optical properties also exhibit superior properties in chemical reactions. The second chapter mainly introduces the density functional theory based on the first principle, including its theoretical framework, development process, time-dependent density functional theory and quantitative response. The theoretical basis of the density functional (DFT) is the quantum mechanics, which is based on the quantum mechanics. Its basic research amount is the electronic density of the system. By solving the Kohn-Sham equation, the interacting multiple particle system is converted into a single particle system without interaction. The energy and density of the system ground state are calculated, and the time-dependent density functional theory with time-dependent perturbation is introduced in the density functional. The electronic structure of the excited state can be more accurately simulated. The final realization of the density functional theory in the application depends on the calculation simulation of the quantitative software package. The third chapter introduces the intermolecular interaction and the molecules. The research of luminescence mainly consists of two tasks: the first work is the enhancement of phosphorescence between the molecular aggregation induced lines. The intermolecular channeling and crossing (ISC) plays an important role in various optoelectronic applications. However, it is very inconvenient to use traditional chemical modification and heavy metal doping to increase the probability of intersystem channeling, which limits its application. In our work, we propose a new type of "AI-ISC" mechanism. In polymer molecules, the energy level division caused by intermolecular interaction can be used to improve the energy level matching between the single and three excited states, and then the probability of the intersystem crossing is improved. In the experimental spectrum, the increasing probability of this enhancement in the molecular aggregates greatly promotes the molecular phosphor emission. At the same time, the phosphor emission also redshifts with the enhancement of the aggregation degree, providing a convenient channel for the adjustment of the phosphorescence wavelength. The second work is the luminescence mechanism of the self assembled organic quantum dots. In this study, a novel quantum dot of organic dye was designed and synthesized. The quantum dot system showed a high fluorescence quantum yield in the solution. The fluorescence yield was lower when the hydrophobic interaction and pion pion accumulated to form solid state, and the luminescence wavelength had a strong dependence on the excitation wavelength. Theoretical calculations found that the quantum dots have a strong dependence on the excitation wavelength. The principle of quantum dots luminescence is that the molecular polymerization in the solution is destroyed, mainly in the form of single molecule. By the action of the solvent, the push-pull charge transfer mechanism is formed, and the luminescence efficiency is influenced. In the solid state, the molecules have pion pion accumulation and H- aggregation, the energy level is split, the molecular vibration is suppressed and the relaxation slows down. In violation of the Kasha's rule, the luminescence wavelength has a strong dependence on the excitation wavelength, while the radiation transition probability of the excited state decreases and the fluorescence quantum yield is reduced. The fourth chapter introduces the study of the charge polarization and the catalytic mechanism caused by the intermaterial interaction, including three work: the first work is the photoluminescence of graphene based composites In this work, we have designed a sandwich structure of C_xN_y and graphene based materials, in which carbon and nitrogen (g-C_xN_y) is sandwiched between two layers of functionalgraphene modified graphene (GR_F). First principle calculation shows that the charge polarization caused by the interaction between g-C_xN_y and GR_F makes this three The Meiji system can capture both ultraviolet and visible light at the same time, and then stimulate the GR_F of the hole moving to the outer layer. Under the help of the photogenerated hole, the water adsorbed on the GR_F occurs cracking, produces protons, is attracted by the C_xN_y electrostatic charge of the aggregated negative charge, the proton transmigrates to the C_xN_y through the graphene, and produces hydrogen under the action of photogenerated electrons. Gas. As the structure of the outer layer of graphene does not allow hydrogen penetration, the hydrogen is separated from the outside and stored in the system. It is known that the sandwich composite system designed by us has realized the integration of photocatalytic hydrogen production and safe hydrogen storage. The second work is the nitrogen doped graphene catalyzed reduction of hydroxyl phenol. In the experiment, through a variety of MOF The material was sintered at high temperature to obtain the multilayer carbon material of nitrogen doped graphene at high temperature and catalyze the reduction of p-nitrophenol. The best catalytic activity of the material containing pyrrole N doped graphene was the best. The theoretical calculation was carried out through the study of the configuration, electronic structure, adsorption and conductivity of three kinds of N doped graphene, and found that doped N atoms Due to the electronegativity difference between graphene and graphene, the charge polarization, charge accumulation and active site are provided after interaction. The active site of positive charge near the active site in pyrrole N doped graphene is the most, the adsorption energy of 4-NP- is the strongest, and the coupling activation degree is higher. The pyrrole N doped graphene system continues the excellent conductivity of graphene materials. It provides a constant source of driving force for the reduction of the reaction. Therefore, pyrrole N doped graphene has a high reaction activity to the catalytic reduction of p-nitrophenol, which is in agreement with the experimental results. The third work is TiO_2-Pd@Pt photocatalytic cracking water. The theoretical and experimental cooperating design and synthesis of the atomic thickness adjustable Pd@Pt shell structure, The shell structure is combined with the N type semiconductor, anatase TiO_2. In this system, the Pd@Pt shell structure has dual functions in the photocatalytic water cracking reaction, which all depend on the atomic thickness of the metal Pt in the composite. The double effects are the increase of the interface charge polarization caused by the interaction of Pd and Pt, respectively. The electron capture on the metal promotes charge separation and increases the adsorption capacity of water by increasing the surface charge density of the Pt and the stress of the lattice. These properties increase the catalytic activity of the photocatalytic cracking water.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.3;O644.1

【相似文献】