【作者】 张振龙；

【导师】 莫育俊；

【作者基本信息】 河南大学 ， 光学， 2004， 硕士

【摘要】 近年来，偶氮类染料的结构研究引起了人们的注意，因为它们是工业上所使用染料的最大类，并且作为酸碱指示剂、氧化还原指示剂、金属显色指示剂在分析化学中有着广泛的应用。另外，偶氮类染料在可逆的光信息存储(全息和数字)得到广泛应用，存储过程就是利用光致偶氮类染料的反式—顺式—反式的异构化过程，从而利用介质折射率的局部变化来进行存储。光致极性和分子结构的变化使偶氮衍生物作为可逆的分子开关器件得以普遍应用。关于偶氮类染料的结构和特性的研究已有不少文献报导，他们主要通过紫外—可见光吸收谱、近红外和拉曼光谱以及光化学方法进行。但还很少有表面增强拉曼散射(SERS)方面的报导。大量研究表明表面增强拉曼散射(SERS)对于研究吸附在金属表面的分子结构及吸附分子与表面的相互作用是非常有力的工具。本论文利用表面增强拉曼散射技术研究了偶氮类染料—4-二甲胺基偶氮苯(4-Dimethylaminoazobenzene，DAB)在同种金属表面不同环境及不同金属表面的的吸附状态，分析环境因素对其分子结构的影响，以获得其分子结构的更多信息。 本论文包括以下五个部分： 第一章简单介绍了表面增强拉曼散射现象的发现、特点、机理及其发展应用。 第二章研究了DAB分子在不同衬底，即银胶、银镜和铜表面SERS光谱。结果表明DAB分子都是通过二甲胺基吸附于金属表面，但不同情况下，其吸附状态不同。在银胶中，其结构为稳定的反式结构，而在银镜表面，其结构由反式转变为顺式结构，这主要是由于溶液中水分子和空气中气体分子对DAB分子作用的差别。在银镜和铜表面SERS光谱也有所不同，这是由于银镜的增强能力比铜大。 第三章研究了DAB分子在不同PH值银胶溶液中的SERS光谱。当溶液PH值小于4时，由于质子化，DAB分子将从偶氮型结构转变为醌型结构，本章利用SERS技术，研究了其结构的这种变化，并且发现这种结构的变化是可以逆转的。河南大学光学专业2001级硕士论文DAB分子在不同PH值溶液中与银纳米颗粒相互作用有所区别，这是由于二甲胺基的N原子带上了正电荷。 第四章研究了DAB分子的单分子SERS光谱。我们采用一种简单的方法，将含有DAB分子的银胶体溶液滴在铝箔上，激发光聚焦在液滴上直接进行测量，观察到了分子SERS信号的“Blinking”现象，并首次报道了其SERS拉曼频移随时间产生波动，这是由于个体分子和银纳米颗粒的相互作用及其在银纳米颗粒表面的l吸附状态不同而导致的。另外，统计分析表明分子拉曼信号服从泊松分布。这些表明在常温和常规条件下得到了DAB分子的单分子SERS光谱。 第五章研究了维生素B，:的SERS光谱。维生素BI:的拉曼光谱在低波数直到现在未见报道。本章利用表面增强拉曼散射技术获得了维生素B，:在全波数的SERS光谱，这对于利用SERS技术进行维生素BI:的检测及其他药物检测具有重要的参考价值。更多还原

【Abstract】 The structure of azo dyes has attracted considerable attention in recent times, since they represent the largest class of dyes used in industry, and also has extensive applicability in analytical chemistry as acid-base, redox and metallochromic indictors. Moreover, azo dyes find wide applicability in reversible optical data storage. The storage process utilizes the light induced trans-cis-trans isomerization of the azo dye, thereby utilizing the local variation of the refractive index of the medium. The photoinduced changes in polarity and molecular structure have led to widespread application of azobenzene derivatives as reversible molecular switch devices. 4-Dimethylaminoazobenzene (DAB) is an important azo dye, which is used to the production of color polishes, wax products, polystyrene, and soap. It is also used as a chemical indicator for free hydrogen chloride (HC1) in juice, as a spot test identification of peroxidized fats, and as a PH indicator. There were many literature on the studies of the structure of DAB by means of various spectroscopic and photochemical methods including UV-Vis absorption, infrared (IR), and Raman. While very few reports on the SERS of DAB appeared. Surface-enhanced Raman scattering (SERS) is widely used as a highly powerful analytical tools to investigate molecular structure and interaction between molecules and metal surface resulting in strongly increased Raman signals from molecules which have been attached to nanometer sized metallic structures. The SERS spectra of DAB adsorbed on the same substrate in different environment and on different substrate were investigated in this paper. The objective of this work was to obtain information about the spectral properties of DAB and use these information to gain an overall picture of the nature of the adsorption sites on these metal surfaces.This paper includes five sections as following:In the first section, the discovery, characteristics, mechanisms, and recent developments of SERS are simply summarizedIn the second section, the SERS spectra of DAB molecules adsorbed on silver sol, silver mirror, and copper were investigated. The analysis of spectra shows that DAB molecules adsorbed on the metal surfaces through the Dimethylamino group, but the adsorptions of DAB molecules were different in varied environment. For instance, the structure of DAB in silver sol is a stable cis form, while that is an unstable trans form on silver mirror, which could be due to the difference of interaction between the solvent molecules and DAB molecules. The difference of SERS spectra of DAB adsorbed on silver mirror and copper could be due to the difference of apparent enhanced factors of them.In third section, the SERS spectra of DAB in silver sol with varied PH values were obtained. When the PH of the solution was lower than 4, the structure of DAB changes from an azo type to a quinoid type. This change was studied by SERS and the reversibility of transformation was found. In addition, the interactions between DAB molecules and silver particles in varied PH values were different, which is mainly due to the N atom in Dimethylamino group positively charged.In the forth section, the SERS spectra of single DAB molecule were recorded. SERS spectrum of single DAB molecule under normal temperature and condition was reported in this section by a simple method, in which the sample was prepared by mixing 4-dimethylaminoazobenzene with silver colloid and SERS spectra were directly recorded from the sample droplet on the aluminum foil. Blinking of the SERS spectra and the Poisson statistical distribution of the Raman signal were observed. Moreover spectral diffusion of Raman shift with time was reported by the first time according to our knowledge, which could be due to the difference of interaction between varied single molecules and varied silver particles surface, for instance, due to the differentadsorption states of DAB molecules on the silver surface, which should be a powerful evidence for single molecule detection by SERS.更多还原