N-ethyl Sulfonyl Pyrene-n'-propyl Triethoxy Silane Urea Synthesis And Photophysical Studies Of Aggregation Behavior

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.