Pyrene Mark The Synthesis Of Organic Siloxane Hydrolysis And Condensation Process

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.According to the effects of organic substituent,the structures and properties of sol-gel materials can be modified,accompanied with the function of composite materials being enlarged.The nature of the local microenvironment within a sol-gel-derived nanocomposite is an important factor in designing materials for sensing or photonic applications.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.There are many modern methods employed to obtain the information during the sol-gel process,such as ¹H NMR,FT IR,SAXS,XRD and photophysical techniques.In these instances,fluorescence spectroscopy is the method of choice as it reports on the local microenvironment surrounding a probe molecule.Fluorescent probes can be introduced into the material either as a dispersed dopant or as part of the silica network via covalent attachment, thereby sensing different regions of the material.Furthermore,the probe may be bound to or intrinsically part of an entrapped biomolecule,allowing for studies of biomolecule conformation, accessibility,and dynamics within biologically active nanocomposite biomaterials.There have been much more issues focused on the fluorescien as a physical probe,on the other side,less attention have been paid on the labled siloxane,which may be more important in the materials synthesis.With emphasis on the insights above mentioned,we carried out the research in this thesis mainly including five parts:[1]A novel compound which contains a fluorescence moiety and a siloxane head named N-ethylsulfonylpyrene-N'-ethyltriethoxysilane ureide were designed and synthesized.The ¹H NMR and FT IR spectra confirmed the component of the product.[2]The pyrene moiety afford convenience that we need not add any other fluorescence probes more into the sol-gel system.The materials were formed as the precursors undergo hydrolysis and condense reaction,when the pyrene moiety became part of the network.The in-situ stationary fluorescence spectroscopy was used to follow the hydrolysis and condensation of pyrene labled siloxane in different situation.The following conclusions were proposed.When the TM dissolved in the CH₂Cl₂ then added to bulk pure water,the emission intensity markedly increased as the time increasing,while the profile of spectra remained.The acid environment led to stronger fluorescence intensity,but less increasing as the time increasing.The results indicate the TM have poor solubility in the water,thus the monomeric emission plays an important role.There is no evidence of the aggregates of perene in the fluorescence spectra.The differences of two system show the TM had better solubility in the acid environment,the hydrolyzed product,that like the surfactant molecules, may be easily form under the acid catalysis then leave the organic phase to stay in water.This result disagreed with the viewpoint that the TM may undergo self- organization proposed from its molecular conformation.We can conclude that the hydrolysis reaction had been taken place,while the condensation reaction was not obvious.This should be ascribed to the non-linear molecular conformation in the solution,the Si-OH heads were difficult to condense.Although the condense reaction had taken place,the hydrogen bond intra molecules made the pyrene moiety can not close easily,then little aggregates in the system.The FT IR spectra confirmed this conclusion.The changes in the FT IR spectra as the time increasing show that the system have novel interaction because the absorption bands located at 1 655 and 1 560 cm^-1 shifted to 1 450 and 1 370 cm^-1.The particular changes can be ascribed to the protonizing of N atom in ureide.The conclusion was confirmed in several papers.[3]Instead with ethanol and basic catalyst,the fluorescence spectra reveal distinct transformation as the time increasing.Compared with the system above,the changes in fluorescence spectra were as following:in the first one hour,the emission band around 420 nm of overlap pyrenes appeared,and the spectra were constant.This phenomena indicates the TM can hydrolysis and condense easily under basic catalysis,the product was more rigid and compact,that constrain the free movement of the pyrene moiety.The SEM images confirmed the compact framework.[4]The TM was doped into the TEOS process under basic catalysis.The fluorescence spectra supplied much useful information.As the time increasing,a emission band around 470 nm indicated the "sandwich-like" pyrene presence.This result accounts for the presence of TEOS accelerated the hydrolysis and condense reactions of TM and TEOS because of the low steric.Meanwhile,the insert of TEOS destroy the hydrogen bond,thus the spacer in the TM was more flexible,the adjacent pyrene moiety can form more "sandwich-like" aggregates.The SEM images show the co-condensed material were cross-link net structure based on many nanospheres.The morphology were induced by the TEOS,which can form resemble morphology.The presence of TM endowed the material the hydrophobic property,that force co-condense product to form the spheres to decrease the surface pressure.The SiO₂ connect the spheres to form network.The presence of TM in the composite material was confirmed by the fluorescence microscope.[5]The PSEDA,a mid-product during the synthesis of pyrene labled siloxanes,was employed to discuss the self-organization and mutual of a anionic surfactant --- sodium dodecyl sulfate(SDS). We have the fluorescense emission spectra of PSEDA in different surfactant concentrations.At a concentration well below the CMC(10^-6～10^-4 mol·L^-1),the quenching of PSEDA could be explained by considering an ionic complex formation.Here,the complexation took place between the protonated form of the probe molecules and the negatively charged surfactant monomers.When the surfactant concentration approached close to but below the CMC(10^-3 mol·L^-1),the appearance of a new broad band at 480 nm mean the formation of an excimer.This could be ascribed to the formation of undefined aggregates between the surfactant molecules and the fluorophores and this has been documented as a premicellar effect.The ratio of excimer to monomer increased with the surfactant concentration and reached a maximum at a particular concentration of the surfactant.The results show that the PSEDA would be a very effective probe in discussing the self-organization process of surfactant molecular.