N-乙基磺酰芘-N’-丙基三乙氧基硅烷脲合成及其簇集行为的光物理研究

【作者】 高阳；

【导师】 胡道道；

【作者基本信息】 陕西师范大学 ， 材料学， 2011， 硕士

【摘要】 利用有机修饰硅氧烷作为前驱体经由溶胶-凝胶过程制备各种各样的有机-无机杂化材料成为近年来的研究热点。丰富的可修饰性使这类材料具有极其优越的多功能化特点,以及这类杂化材料具有化学稳定、光学透明、机械性能优越等特点,因而被广泛应用于光学器件、电子元件、化学生物医学传感、催化、功能涂层和薄膜等领域。有机修饰硅氧烷中取代基结构和性质的差异会导致前驱体溶胶-凝胶过程的变化。取代基效应具体表现在对水解-缩聚反应速度、产物分布、空间结构演化、存在状态、组织排布方式、产物微区环境的影响。因此,研究硅氧烷在水解初期的分子组织行为对于设计溶胶-凝胶的材料性能和后期制备具有重要的理论价值。荧光探针和荧光标记技术成为有机硅氧烷水解缩合过程中物种分布和结构演化检测的有力工具,能够从微观尺度上探测到分子在溶液相、固-液界面以及固相中的组织行为,具有其它技术无法替代的优势。本实验室以2-萘酚、芘、芘磺酸盐等荧光活性物种作为分子探针监测一系列有机硅氧烷在水解初期阶段的分子组织行为,总结了取代基的长短、亲疏水性影响硅氧烷水解产物在溶液中组织行为的规律性。以上工作都借助荧光探针技术,未有将荧光活性物种共价结合到分子中。本论文在以上研究工作的基础上,实现了两个方面的创新：首先,从荧光标记概念出发,将活性物种芘分子共价键合到长链有机硅氧烷分子的尾端,不仅可以作为信号元素,而且芘分子较强的疏水作用可以调试硅氧烷水解产物的分子行为。其次,模型分子中含有磺酰胺基和酰胺基等极性基团,可在酸性溶液中质子化,通过静电相互作用使分子间彼此排斥；可与类似的极性分子,如二元羧酸分子形成氢键作用,通过小分子的结构“嵌入”,对水解分子的空间排布起到“分子撑”的隔离效应。因此,通过调节溶液的pH值、引入结构“嵌入”型分子,用以调节硅氧烷水解分子的空间分布。具体的研究内容如下：[1]设计合成了N-乙基磺酰芘-N’-丙基三乙氧基硅烷脲(TM),即一端有荧光生色团芘,另一端为可以发生水解缩合的硅氧烷基团的荧光标记有机硅氧烷前驱体。建立合成该化合物的方法,利用红外光谱、核磁共振谱等手段对其进行表征,结果相互自洽,表明所得产物与本研究所设想的结果一致。[2]以N-乙基磺酰芘-N’-丙基三乙氧基硅烷脲(TM)为模型分子,利用荧光光谱对TM水解产物在不同介质溶液中的分子行为进行了系统研究。研究发现：芘荧光分子在不同的酸性溶液中,荧光发射光谱的精细结构相似,单体发射峰占主导地位,最大发射位于470 nm处由芘形成三明治结构的二聚体出现的无精细结构的激基缔合物发射峰(E2)并未观察到,说明在酸性溶液中硅氧烷水解产物分子能够均匀分散到介质中,未发生簇集行为。产生以上结果的原因被归结为酸性条件下,水解分子中的磺酰胺以及碳酰胺均可被质子化,较强的静电排斥作用远大于芘分子的疏水相互作用,因此分子间相互远离。当增加溶液中的pH值,尤其是pH值增加到13时,11和15发射峰强度发生了明显的变化,I1/I5值降低,而且由芘部分重叠而产生的无精细结构的激基缔合物发射峰(E1)具有增强的趋势,说明随着碱性的增加,芘分子周围微环境的极性有所降低,芘分子之间有所靠近。碱性条件下的实验现象进一步说明了水解产物极性基团质子化的隔离效应。[3]为了更深入的研究该硅氧烷水解产物的分子组织行为,我们将该硅氧烷化学键合到活化的石英玻片上,从而对该水解分子起到了固定化作用。固定化作用一方面提高了单位面积中芘分子的浓度,从而易于观察到二聚体的生成,更重要的是相对于分子在溶液相的三维运动而言,固定化之后分子在二维空间的运动为分子构象转变、与小分子的识别作用方面的研究提供了更简化而易于操作的模型。研究发现：将目标分子N-乙基磺酰芘-N’-丙基三乙氧基硅烷脲共价键合到活化的石英玻片上,得到了相对于溶液相较高的分子浓度。固定化后的芘分子光物理行为相对于溶液相发生了明显的改变,二聚体形成的激基缔合物发射峰占据主要地位,而单体峰发射相对较弱。向体系中引入极性水和乙醇溶剂、不同碳链长度的二元羧酸溶液以及含有羟基的硅醇,对分子的簇集行为施加影响,结果发现短碳链的二元羧酸以及含有羟基的硅醇都能够和目标分子结构中的磺酰基、酰胺基形成氢键,起到“分子撑”的隔离效果,从实验现象上导致芘分子荧光光谱中的二聚体发射峰向单体峰转变,以上结论进一步证实了目标分子具有氢键结合作用点,通过改变溶剂和引入特殊结构的小分子可以改变分子的簇集-分散行为。更多还原

【Abstract】 It has been an increasing interest in employing ormosils (organically modified siloxanes) as precursors to prepare various organic-inorganic materials through sol-gel process. These materials with chemical inertness, mechanical stability, optically transparency are becoming more and more widely used in optical and electrical materials, chemical biomedical sensors, catalyst, multifunctional coatings and films, and so forth.The effects of the substituents on the sol-gel chemistry of organotrialkoxysilanes perform specifically on the reaction rate of hydrolysis and condensation, the evolution of species and structure, the molecular self-assembly of hydrolyzed intermediate products and the local microenvironment of sol-gel system. Therefore, systemic and deep researches on the molecular behavior of the hydrolyzate at early stage have important theoretical value for designing and preparing sol-gel materials. The need to understand the nature of the local microenvironments within nanocomposites requires a method that is sensitive to phenomena occurring at the molecular scale, and the fluorescence technique is attractive as it reports on the local microenvironment surrounding a probe molecule. Fluorescent probes can be introduced into organotrialkoxysilanes either as a dispersed dopant or as part of the silica network via covalent attachment, thereby sensing different regions of the material. There have been much more issues focused on the fluorescence as a physical probe in our research group, for instance, pyrene, pyranine and 2-naphthol were used to monitor the progress of sol-gel chemistry of variety of substituent organosiloxanes. The probes are sensitive to evolution of the intermediate structure and the change of fluorescence spectra is alkyl chain-length dependent. The previous work focused on the probe technique and less attention has been paid on the labeled siloxane, which may be more important in the materials synthesis.Based on the above research work, we realized the two aspects of innovation in this paper. Firstly, fluorescent label technique was used in the synthesis of organo-siloxane precursor. The fluorescent species, pyrene, was covalently bond to the long chain of target molecular tail, acting not only as a signal elements, and as a strong hydrophobic terminal group. Secondly, target molecules contain polar group, amide sulfonamides and acylamino, which can be protonated and exclusive to each other via electrostatic interaction in acidic solution. With similar polarity molecules, such as dicarboxylic molecules, which can form hydrogen bonding with amide sulfonamides and acylamino group, the target molecules can be isolated due to the "isolation effect" of the introduced small molecules. Therefore, by adjusting the solution pH value, introducing the "structure-embedded" molecules, the spatial distribution of target molecules could be altered. With emphasis on the insights above mentioned, we carried out the research mainly including the following three parts:[1] A novel compound which contains a fluorescence moiety and a siloxane head named N-ethylsulfonylpyrene-N’-ethyltriethoxysilane ureide was designed and synthesized. The 1H NMR and FT IR spectra confirmed the component of the product.[2] N-ethylsulfonylpyrene-N’-ethyltriethoxysilane ureide was use as target molecules, the molecular behavior during early hydrolysis was systematically studied using fluorescence spectrum. The fluorescence emission spectrum of pyrene was similar in different acid solution, with the dominated monomer emission peaks and none dimmer emission ones. It means the hydrolysis target molecules can be equably dispersed to medium, and the molecular aggregation behaviors were not happened. The above results are attributed to protonation of amide sulfonamides and acylamino and strong electrostatic exclusion, which is far outweigh the hydrophobic interactions between pyrene molecular. When adjusting pH to 13, a marked drop for I1/I5 value and enhanced dimmer emission peak (E1) was observed. It can be explained that the protonation effect of target molecules was weaken with the pH increasing, which leading to a closer distance between the pyrene molecules. The experiment phenomena under alkaline conditions further demonstrated that the protonation of target molecules leads to the isolation effect.[3] In order to further study the molecular organizational behavior, the target molecules were covalently bond to the quartz glass. Immobilization of fluorescent pyrene is known to have strong effects on the photophysical properties. It is found in our work that immobilization can raise the pyrene concentration, thus dimmer of pyrene was easy to generate. On the other hand, the limited mobility in 2D space has provided more simplified and easy operation model for the study of molecular movement than in 3D solution. Indeed, the immobilized molecules behave differently from the ones in solution. The dimmer emissions are dominant, and converted into monomer when polar solvent (water), certain dicarboxylic solution and silanol was introduced. The above results are attributed to hydrogen-bonding between the introduced additives and amide sulfonamides and acylamino group in target molecules. The distance of target molecules can be altered by the structure-insertion of the introduced small molecules, which in turn can recognize certain test objects and can be used as sensing film.更多还原