本文關鍵詞： 能量轉移 相干激子耦合 熒光共振能量轉移 超輻射 集體態(tài) 掃描隧道顯微鏡 掃描隧道顯微鏡誘導發(fā)光 單分子電致發(fā)光 等離激元增強光譜學 脫耦合 卟啉 酞菁　出處：《中國科學技術大學》2017年博士論文　論文類型：學位論文

【摘要】：能量轉移過程是光物理和光化學的核心課題之一,它廣泛存在于各種天然體系和人造體系之中。分子間能量轉移是指能量從供體分子轉移到受體分子的過程。它可以經(jīng)由輻射途徑,通過供體分子輻射出的光子被受體分子重新吸收來實現(xiàn),也可以經(jīng)由非輻射途徑,通過分子間相互作用直接實現(xiàn),而后者的研究更加引起廣泛關注。按照相互作用來源,非輻射能量轉移可以大致分為由于庫倫作用引起的Forster能量轉移和由于電子交換作用引起的Dexter能量轉移。而按照相互作用的強度,又可以分為弱耦合條件下的跳躍轉移和強耦合條件下的相干激子耦合。非輻射能量轉移在人造光收集系統(tǒng)、生物傳感器和有機分子半導體(OLED)等新型領域有重要意義。目前對它的研究主要采用光譜分析和超快激子動力學分析等光學探測手段,而由于受到衍射極限的限制,實空間中納米尺度下分子間能量轉移是如何發(fā)生的很難通過傳統(tǒng)的光學方法研究。掃描隧道顯微鏡(STM)由于其超高空間分辨能力在表面科學和單分子科學中起著重要的作用,而將STM與光學探測手段結合的STM誘導發(fā)光(STML)技術可以實現(xiàn)超過衍射極限的光學分析能力。在本論文的工作中,我們利用高度局域化的STM隧穿電子激發(fā)脫耦合的單個分子,并利用納腔等離激元場的增強效應,得到了亞分子尺度分辨的單分子輻射信息,并進一步以STM單分子操縱和STML為工具,研究了分子二聚體之間相干偶極耦合的方式以及分子多聚體的集體態(tài)的輻射特性。此外,我們還在單分子尺度上初步研究了供體-受體異類分子之間的能量轉移過程。木論文的主要工作分為以下四個部分:在第一章中,我們介紹了本論文所做工作的研究背景和技術基礎。首先,我們簡要介紹了分子激發(fā)態(tài)的失活途徑以及分子間能量轉移的類別,以及能量轉移在新型產(chǎn)業(yè)中的重要作用。然后,我們介紹了 STM的工作原理和STML的研究歷史和現(xiàn)狀。最后,我們描述了實驗中所使用的儀器設備和本論文的主要實驗內(nèi)容。在第二章中,我們首先介紹了單分子電致熒光的實現(xiàn)方法。我們采用多層氯化鈉(NaCl)島作為脫耦合層,隔絕單個鋅酞菁(ZnPc)分子與金屬襯底之間的直接電荷轉移并削弱二者之間的偶極相互作用,并使用銀針尖和銀襯底保證合適的納腔等離激元模式和強度,用隧穿電子激發(fā)分子,實現(xiàn)分子熒光的增強和輸出。由于隧穿電子的高度局域性,我們可以得到具有亞納米分辨能力的分子發(fā)光的實空間的能量分辨光子圖,光子圖的圖案反映了分子躍遷偶極的信息。通過發(fā)光光譜的偏壓依賴關系,我們分析單分子STML機制在小偏壓下是散射機制,在大偏壓下為注入機制。單分子電致熒光的實現(xiàn)使得我們研究分子間相互作用以及分子與等離激元作用成為可能。隨后,我們通過STM操縱構筑了 ZnPc分子二聚體,并測量其STML電致發(fā)光特性。從分子單體到分子二聚體,輻射光譜從單峰結構劈裂為5個峰,且對應的不同能量的實空間光子圖的圖案各不相同。結合理論計算和模擬,我們發(fā)現(xiàn)峰位劈裂來源于相干的分子間偶極-偶極相互作用產(chǎn)生的不同能量的激子態(tài),而二聚體中不同激子態(tài)的實空間光子圖反映了不同取向和不同相位的躍遷偶極耦合模式及其在納腔中的局域輻射特性對于針尖位置的依賴關系。這是第一次在實空間觀察到分子間相干激子耦合的形式,對于研究分子間能量轉移,構建人工光收集體系和分子量子光源提供了思路。在第三章中,我們構筑了具有更多分子單體的ZnPc分子鏈,并研究集體態(tài)的輻射性質。首先,我們關注能量最低的共線同相超輻射模式的輻射特性。通過對實空間光子圖的分析,我們認為分子鏈已經(jīng)可以看作一個相干體系,超輻射激子態(tài)離域在每個單體分子上。我們利用HanburyBrownandTwiss(HBT)裝置測量了分子鏈的超輻射態(tài)發(fā)射光子的二階相關函數(shù),結果表明輻射的光子具有單光子性,這是第一次在實驗上觀察到確定的分子體系的單光子超輻射行為。進一步對輻射的峰位和半峰寬分析符合對于離域激子態(tài)的預期,而STML體系由于其特殊性也表現(xiàn)出和傳統(tǒng)光學測量不完全一樣的展寬變化規(guī)律。隨后,我們又研究了超輻射模式之外的分子相干激子態(tài)的其它輻射模式。通過對不同模式峰位的分析和實空間光子圖的實驗和理論對比,我們也觀察到了分子鏈其它相干耦合模式的特征。我們的結果為分子體系在量子信息領域的應用提供了有用的信息。在第四章中,我們利用單分子STML技術研究異類分子之間的能量轉移過程。首先,通過異類分子二聚體的STML電致光譜與單個分子發(fā)光的對比,我們觀察到了鋅四苯基卟啉(ZnTPP)分子與酞菁(H_2Pc)分子之間存在能量轉移的證據(jù)。隨后,我們把研究的焦點放在了結構更加可控的ZnPc分子與H_2Pc分子組成的供體-受體分子之間的能量轉移上。我們通過單點光譜測量,發(fā)現(xiàn)了能量轉移確定發(fā)生在H_2Pc-Qy→ZrPc-Q→H_2Pc-Qx這三個激發(fā)態(tài)之間,而且能量轉移效率的時序變化以及分子發(fā)光峰位的移動證明了偶極作用在能量轉移中的關鍵作用。最后,我們還研究了 ZnPc-ZnPc-H_2Pc三聚體的輻射特性。我們發(fā)現(xiàn)在ZnPc分子上激發(fā)可以看到類似ZnPc-ZnPc二聚體的發(fā)射特征,這表明兩個ZnPc分子單體間的激子耦合速率遠大于ZnPc-H_2Pc分子間能量轉移速率。但是,我們發(fā)現(xiàn)當激發(fā)最邊上的ZnPc分子時還能看到H_2Pc的輻射光譜,即使在此時針尖已經(jīng)距離H_2Pc分子相當遠的距離。其中的能量轉移機制還需要進一步分析。在單分子尺度上研究異類分子(供體-受體分子)間能量轉移可以為分子光電器件的設計與研發(fā)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.

【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：O561

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