分子间能量转移的空间高分辨研究

发布时间：2018-03-01 01:04

本文关键词：能量转移相干激子耦合荧光共振能量转移超辐射集体态扫描隧道显微镜扫描隧道显微镜诱导发光单分子电致发光等离激元增强光谱学脱耦合卟啉酞菁　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：能量转移过程是光物理和光化学的核心课题之一,它广泛存在于各种天然体系和人造体系之中。分子间能量转移是指能量从供体分子转移到受体分子的过程。它可以经由辐射途径,通过供体分子辐射出的光子被受体分子重新吸收来实现,也可以经由非辐射途径,通过分子间相互作用直接实现,而后者的研究更加引起广泛关注。按照相互作用来源,非辐射能量转移可以大致分为由于库伦作用引起的Forster能量转移和由于电子交换作用引起的Dexter能量转移。而按照相互作用的强度,又可以分为弱耦合条件下的跳跃转移和强耦合条件下的相干激子耦合。非辐射能量转移在人造光收集系统、生物传感器和有机分子半导体(OLED)等新型领域有重要意义。目前对它的研究主要采用光谱分析和超快激子动力学分析等光学探测手段,而由于受到衍射极限的限制,实空间中纳米尺度下分子间能量转移是如何发生的很难通过传统的光学方法研究。扫描隧道显微镜(STM)由于其超高空间分辨能力在表面科学和单分子科学中起着重要的作用,而将STM与光学探测手段结合的STM诱导发光(STML)技术可以实现超过衍射极限的光学分析能力。在本论文的工作中,我们利用高度局域化的STM隧穿电子激发脱耦合的单个分子,并利用纳腔等离激元场的增强效应,得到了亚分子尺度分辨的单分子辐射信息,并进一步以STM单分子操纵和STML为工具,研究了分子二聚体之间相干偶极耦合的方式以及分子多聚体的集体态的辐射特性。此外,我们还在单分子尺度上初步研究了供体-受体异类分子之间的能量转移过程。木论文的主要工作分为以下四个部分:在第一章中,我们介绍了本论文所做工作的研究背景和技术基础。首先,我们简要介绍了分子激发态的失活途径以及分子间能量转移的类别,以及能量转移在新型产业中的重要作用。然后,我们介绍了 STM的工作原理和STML的研究历史和现状。最后,我们描述了实验中所使用的仪器设备和本论文的主要实验内容。在第二章中,我们首先介绍了单分子电致荧光的实现方法。我们采用多层氯化钠(NaCl)岛作为脱耦合层,隔绝单个锌酞菁(ZnPc)分子与金属衬底之间的直接电荷转移并削弱二者之间的偶极相互作用,并使用银针尖和银衬底保证合适的纳腔等离激元模式和强度,用隧穿电子激发分子,实现分子荧光的增强和输出。由于隧穿电子的高度局域性,我们可以得到具有亚纳米分辨能力的分子发光的实空间的能量分辨光子图,光子图的图案反映了分子跃迁偶极的信息。通过发光光谱的偏压依赖关系,我们分析单分子STML机制在小偏压下是散射机制,在大偏压下为注入机制。单分子电致荧光的实现使得我们研究分子间相互作用以及分子与等离激元作用成为可能。随后,我们通过STM操纵构筑了 ZnPc分子二聚体,并测量其STML电致发光特性。从分子单体到分子二聚体,辐射光谱从单峰结构劈裂为5个峰,且对应的不同能量的实空间光子图的图案各不相同。结合理论计算和模拟,我们发现峰位劈裂来源于相干的分子间偶极-偶极相互作用产生的不同能量的激子态,而二聚体中不同激子态的实空间光子图反映了不同取向和不同相位的跃迁偶极耦合模式及其在纳腔中的局域辐射特性对于针尖位置的依赖关系。这是第一次在实空间观察到分子间相干激子耦合的形式,对于研究分子间能量转移,构建人工光收集体系和分子量子光源提供了思路。在第三章中,我们构筑了具有更多分子单体的ZnPc分子链,并研究集体态的辐射性质。首先,我们关注能量最低的共线同相超辐射模式的辐射特性。通过对实空间光子图的分析,我们认为分子链已经可以看作一个相干体系,超辐射激子态离域在每个单体分子上。我们利用HanburyBrownandTwiss(HBT)装置测量了分子链的超辐射态发射光子的二阶相关函数,结果表明辐射的光子具有单光子性,这是第一次在实验上观察到确定的分子体系的单光子超辐射行为。进一步对辐射的峰位和半峰宽分析符合对于离域激子态的预期,而STML体系由于其特殊性也表现出和传统光学测量不完全一样的展宽变化规律。随后,我们又研究了超辐射模式之外的分子相干激子态的其它辐射模式。通过对不同模式峰位的分析和实空间光子图的实验和理论对比,我们也观察到了分子链其它相干耦合模式的特征。我们的结果为分子体系在量子信息领域的应用提供了有用的信息。在第四章中,我们利用单分子STML技术研究异类分子之间的能量转移过程。首先,通过异类分子二聚体的STML电致光谱与单个分子发光的对比,我们观察到了锌四苯基卟啉(ZnTPP)分子与酞菁(H_2Pc)分子之间存在能量转移的证据。随后,我们把研究的焦点放在了结构更加可控的ZnPc分子与H_2Pc分子组成的供体-受体分子之间的能量转移上。我们通过单点光谱测量,发现了能量转移确定发生在H_2Pc-Qy→ZrPc-Q→H_2Pc-Qx这三个激发态之间,而且能量转移效率的时序变化以及分子发光峰位的移动证明了偶极作用在能量转移中的关键作用。最后,我们还研究了 ZnPc-ZnPc-H_2Pc三聚体的辐射特性。我们发现在ZnPc分子上激发可以看到类似ZnPc-ZnPc二聚体的发射特征,这表明两个ZnPc分子单体间的激子耦合速率远大于ZnPc-H_2Pc分子间能量转移速率。但是,我们发现当激发最边上的ZnPc分子时还能看到H_2Pc的辐射光谱,即使在此时针尖已经距离H_2Pc分子相当远的距离。其中的能量转移机制还需要进一步分析。在单分子尺度上研究异类分子(供体-受体分子)间能量转移可以为分子光电器件的设计与研发提供思路。
[Abstract]:The energy transfer process is one of the core issues of photophysics and photochemistry, it widely exists in all kinds of natural system and artificial system. The intermolecular energy transfer refers to the transfer of energy from the donor molecule to the receptor molecule. It can pass through the photon radiation, radiation emitted by the donor molecule receptor molecules to achieve re absorption, too through the non radiative pathway through intermolecular interactions directly achieved, whereas the latter studies pay more attention to the interaction. According to sources, non radiation energy transfer can be roughly divided into the Kulun for energy transfer caused by Forster and due to electron exchange effect of Dexter energy transfer. And according to the intensity of interaction, and can be divided into coherent exciton coupling under weak coupling condition jump and strong coupling. Under the condition of non radiative energy transfer in artificial light collection system, Biosensor and molecular organic semiconductor (OLED) plays an important role in the new field. The research of it is mainly used in spectral analysis and dynamic analysis of ultrafast exciton optical detection means, due to the diffraction limit, the real space energy transfer between molecules in nano scale how it is difficult to study the traditional optical method the scanning tunneling microscope (STM) due to play an important role in surface science and single molecular science of its high resolution space, and combining the STM and optical detection method of STM induced luminescence (STML) technology can realize optical beyond the diffraction limit analysis. In this paper, we use the the highly localized STM tunneling electron excitation and single molecule coupling, and the use of nano cavity plasmon polaritons field enhancement effect, obtained a single sub molecular resolution radiation signal Of interest, and further to STM molecule and STML as a tool to study the molecular radiation characteristics of poly two collective state between the coherent dipole coupling way and molecular polymer. In addition, we are still single molecular scale preliminary energy transfer process between the donor acceptor molecules. The main research of heterogeneous wood work this paper is divided into the following four parts: in the first chapter, we introduce the research work done by the background and technical basis. Firstly, we briefly introduced the molecular excited state deactivation pathways and the type of intermolecular energy transfer, the energy transfer and an important role in the new industry. Then, we introduce the research history and present status of the working principle of STML and STM. Finally, we describe the use of the equipment and main research contents of the thesis. In the second chapter, we first introduce a single Realize method electrofluor. We use multi-layer sodium chloride (NaCl) and the island as a coupling layer, isolated single zinc phthalocyanine (ZnPc) direct charge transfer between the molecule and the metal substrate and the interaction between the two and the weakening of the dipole, using needle tip and silver substrate ensure appropriate nanocavity plasmons pattern and intensity by tunneling electron excited molecules, molecular fluorescence enhancement and output. Due to the highly localized electron tunneling, we can get the real space with sub nanometer resolution molecular luminescence energy resolved photon, photon map pattern reflects the dipole transition information. Through the bias light the spectral dependence, we analyze the single molecular mechanism of STML is the scattering mechanism under small biases, as the injection mechanism under the large bias. Single molecule fluorescence power allows us to study the interactions between molecules and With the plasmon effect possible. Then, we constructed the ZnPc molecules by STM manipulation of two dimers, and measured the STML electroluminescence characteristics. From monomer to dimer molecule two, radiation spectrum from a single peak structure splits into 5 peaks, and the corresponding different space between light energy subgraph patterns are different. According to the theoretical calculation and simulation, we found that the peak split from the coherent molecular dipole dipole interaction between the different energy of excitons, real space photon map and two different exciton states in poly body reflects the radiation characteristics of transition dipole coupling mode of different orientations and different phase and localized in the nanocavity in dependence on the position of the needle tip. This is the first time in the real space observed intermolecular coherent exciton coupling form, for the study of intermolecular energy transfer, the construction of artificial light collection system and the molecular weight of the son Provides the idea of light. In the third chapter, we construct the ZnPc molecular chain with more monomer, and Study on the radiation properties of set body. Firstly, we focus on the radiation characteristics of the lowest energy phase collinear superradiant modes. Based on the analysis of the real space photon map, we think the molecular chain is regarded as a coherent system, super radiation exciton delocalization in each monomer molecule. We use HanburyBrownandTwiss (HBT) two order correlation function device for measuring ultra radiation emission photon molecular chain, the results show that the radiation photon with single photon, this is the first time observed in experiments of single photon molecular system the super radiation behavior. Further peak position and half peak width of radiation analysis for delocalized exciton states in line with expectations, but the STML system due to the particularity of the show and the traditional optical measurement is not entirely a Broadening variation of samples. Then, we study the radiation pattern of other molecules beyond the radiation pattern of the coherent exciton states. By comparing experimental and theoretical models of different peak analysis and real space photon map, we also observed the molecular chain of other coherent feature coupling model. Our results provide useful information for the application of the molecular system in the field of quantum information. In the fourth chapter, we use the transfer process between the single molecule STML technology to study the heterogeneous molecular energy. Firstly, through the comparison of two heterogeneous molecular poly STML electroluminescent spectra with a single molecule, we observed the zinc porphyrin (four ZnTPP) and phthalocyanine (H_2Pc) molecules exist evidence of an energy transfer between molecules. Then, we focus on the ZnPc between the molecule and the molecular structure of H_2Pc is more controllable consisting of donor acceptor molecules The transfer of energy. We through a single point spectrum measurement, we found that the energy transfer is determined between H_2Pc-Qy to ZrPc-Q and H_2Pc-Qx of the three excited state, and the temporal variation of the energy transfer efficiency and mobile molecular luminescence peak proved the key role of the dipolar interaction in energy transfer. Finally, we also study the radiation the characteristics of ZnPc-ZnPc-H_2Pc trimer. We found that can see emission characteristics similar to the ZnPc-ZnPc two dimer excitation in the ZnPc molecule, which indicates that the exciton coupled rate of two ZnPc molecules between monomers is far greater than the rate of energy transfer between ZnPc-H_2Pc molecules. However, we found that when the excitation of the ZnPc molecules can also see the end of the radiation spectrum of H_2Pc at this time, even if the needle is from the H_2Pc molecule gooddistance. Energy transfer mechanism which needs further analysis. Research in single molecular scale The energy transfer between the heterogeneous molecules (donor receptor molecules) can provide an idea for the design and development of molecular optoelectronic devices.

【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】：O561

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