Dynamics And Spectroscopy Research Of Single Molecules At Room Temperature

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.