【作者】 董双丽；

【导师】 肖连团； 贾锁堂；

【作者基本信息】 山西大学 ， 原子与分子物理， 2009， 博士

【摘要】 在最近二十多年来,单分子光谱的研究由于在量子信息、光化学、生物学以及纳米材料科学等领域中的广泛应用引起了人们的极大兴趣。在一个典型的系综实验中,单分子系统的不同动力学特性被大量平均,其结果是相关参数的平均值。通常采用的系综测量中的许多理论内容和模型不能够描述单分子光谱。单分子是一个能够用来研究量子动力学效应的简单体系,单分子光谱不含有任何系综平均,能够产生非常精细的动力学性质的信息。在应用单分子光谱研究单分子系统的动力学过程中,发现了许多新颖的实验现象,包括单分子谱线的随机变化、荧光间断现象、单分子斯塔克效应、光子聚束和反聚束现象等。室温下工作的单分子系统由于对光子的收集效率较高,对应光子强度统计呈亚泊松强度分布特性,而且具有便于实际应用的优势得到了关注。研究室温单分子量子动力学特性,并进行可靠的观测和控制是进一步应用单分子于量子信息领域的先决条件。本论文主要针对室温条件下掺杂于聚合体薄膜中的单个染料分子的荧光探测进行了理论分析和实验研究;分析了单分子时间分辨光子计数光谱的最佳信号噪声比;基于单事件光子统计以及Mandel’s Q-参数分析给出了一种快速有效的单分子判别方法;根据测量得到的室温下PMMA薄膜中Cy5染料荧光分子的光子计数光谱分析了单个Cy5分子的激发态寿命和三重态的驰豫时间。使用化学结构对称扁平、发光效率高以及存活时间长的SR荧光分子作为探测对象,进一步研究了单分子的动力学特性。本论文工作的创新点:1.基于标准的HBT测量方式以及单事件光子统计,通过对实际单分子信号源和理想双分子信号源的荧光统计特性的分析,给出单分子系统的判别方法。依据(?),仅需要几百毫秒的测量时间以及大约探测10~4个荧光光子就可以快速判断光子源是否为单分子系统,对所提出判据的合理性、有效性进行了分析。2.通过光子计数光谱在不同信号背景比下的最佳信号噪声比分析,讨论单分子荧光背景信号分别为时间均匀分布和指数特性分布时同步取样时间门的选取。测量了室温下PMMA薄膜中Cy5荧光分子的时间分辨光子计数光谱,分析得到单个Cy5荧光分子的激发态寿命间于1.6 ns到2.0 ns之间,对三重态的布居时间进行了分析。研究了单分子光漂白时间和光子产率对激发强度的依赖特性。3.通过测量两个正交偏振探测通道的荧光光子关联强度所得到的偏振度值标定单分子偶极再取向的变化。对室温下聚合体薄膜表面的单个SR荧光分子的偶极取向进行测量及跟踪,测量单分子偶极再取向行为,发现偶极再取向具有在多个偏振态之间的量子化跳跃特性,且分子的转动关联时间τ_R在55 ms附近出现的概率最大。4.以SR荧光分子作为探针分子,分别测量聚合体薄膜表面、薄膜内部以及超冷液体的动力学特性。探测发现薄膜表面的荧光分子表现出快速的转动行为,反映了聚合体薄膜表面活跃的动力学特性。镶嵌在薄膜内部的荧光分子受到环境的束缚,自由度低,主要表现出单分子三重态的影响,测量得到三重态驰豫时间约0.2 ms。液体中的荧光分子具有多重自由度,表现出明显的扩散行为,SR荧光分子在Glycerol溶液中的扩散特征时间是1.1 s。更多还原

【Abstract】 In about 20 years, single-molecule spectroscopy has evolved from a specialized variety of optical spectroscopy into a versatile tool used to address a broad range of questions in physics, chemistry, biology, and materials science. In a typical ensemble experiment, many molecules are probed at the same time and therefore such a measurement can only yield the average behavior of the molecular dynamics. A single molecule is a simple system which can be used to research the quantum dynamics. The study of single molecules completely eliminates ensemble averaging, and therefore offers the most refined dynamics information about the molecules and surroundings.In optically detection experiments, a variety of phenomena not seen in ensembles have been discovered in single-molecule spectroscopy including dynamic spectral shifts, discrete jumps in fluorescence intensity due to intersystem crossing, single-molecule Stark effects, and photon bunching and anti-bunching. At room temperature single molecules experiment has higher fluorescence collection efficiency, and the photon counting distribution exhibits a sub-Poissonian photon statistics behavior. The single molecules optically detection experiments and applications are more simple and actual at room temperature.One important presupposition of single-molecule application in quantum information fields is to investigate, measure and control the single molecules quantum dynamics. The main contents of this thesis are theoretically analysis and experimental study of single dye molecules fluorescence detection. Signal-to-noise ratio of time-resolved spectroscopy of a single molecule is analysed by using time-gated techniques. Based on single-molecule photobleaching phenomenon, we present a fast and robust method to recognize single molecules by using single events photon statictics and Mandel’s Q-parameter. With single molecular time-resolved photon counting spectroscopy, we measure the fluorescence lifetime and on/off-state lifetime of single Cy5 molecules adulterated in PMMA films. And the single-molecule dynamics are researched by using of flat SR molecules.The innovations of this paper:1. By use of Hanbury-Brown-Twiss method and the single events photon statictics, it is shown that the Q-parameter of an assumed ideal double-molecule fluorescence with the same average photon number as that of the sample fluorescence can act as the criterion for single-molecule recognition. When , only need hundreds ms measurement time and about 10~4 fluorescence photons to recognize a single molecules system. The influence of signal-to-background ratio and the error estimates for photon statistics are also presented.2. Based on optimal signal-to-noise ratio analysis of photon counting spectroscopy with different signal-to-background ratio, it is found that optimal signal-to-noise ratio can be obtained by choosing an appropriate gate time with a certain optical background. Using single molecular time-resolved photon counting spectroscopy, we measure the fluorescence lifetime and triplet state lifetime of single Cy5 molecules in PMMA polymer film. And the influence of excited intensity on single molecules photobleaching and photon yield is measured experimentally.3. The reorientational information of the in-plane component of the molecular absorption dipole moment can be obtained based on polarization measurements for emission fluorescence. The dipole orientational jumps of single dye molecules adsorbed onto polymer films are presented and the rotation correlation time is about 55 ms mostly. 4. Single SR molecules fluorescence is detected in polymer film, on polymer surface and in supercooled liquid respectively. It is found that the single molecules on polymer surface have vivid reorientation dynamics at room temperature, which indicates the dynamic characteristic of polymer surface. The molecules in polymer are immobile and just showing the effects of intersystem crossing with the triplet state lifetime of 0.2 ms. And a clear diffusing behavior is observed for single molecules in liquid with diffusing time of 1.1 s for SR fluorescence molecules in Glyserol.更多还原