Preparation And Properties Of The Hybrid Materials Functionalized By Diacetylenes And Polydiacetylenes

Diacetylenic groups possess π-electronic systems,and are electron-rich groups.Polydiacetylenes(PDAs)can be prepared through the topochemical polymerization of self-assembled diacetylene(DA)monomers under ultraviolet(254 nm)or y-irradiation.Polydiacetylenes(PDAs)belonging to a unique family of conjugated polymers with the π-electron delocalization along the alternating ene-yne conjugated backbone,thus PDAs have unique optical and electronic properties.PDAs could display an intense chromatic transition in response to various external stimuli,and the distinct color change can be easily perceived by the naked eye,making PDAs ideal candidates for chemical or biological sensors.In addition,the sensing applications of PDAs would be expanded by introducing additional meritorious features into the PDAs system to prepare a PDAs sensor with a specific sensing performance.Periodic mesoporous organosilicas(PMOs)are functional organic-inorganic hybrid materials,in which the bridged organic groups are covalently embedded within the silica framework without plugging the mesopores.PMOs have ordered mesoporous pore channels,larger specific surface areas,pore volumes,and organic functional groups covalently embedded in the pore walls,which ensure the potential use in catalysis,adsorption,biomedicine,optoelectronic materials,and sensing.In this thesis,diacetylene-bridged silsesquioxane and bis-diacetylene-bridged silsesquioxane were prepared based on diacetylene.Diacetylene-bridged periodic mesoporous organosilicas nanoparticles and films were synthesized using a cationic trimeric surfactant as the structure-directing agent through the co-condensation and evaporation-induced self-assembly process,respectively.Then polydiacetylene-based periodic mesoporous organosilicas(PDAPMOs)films were obtained through the topochemical polymerization of diacetylenic groups in diacetylene-bridged periodic mesoporous organosilicas films by irradiation with ultraviolet light(254 nm).Structural characterizations of the materials were obtained by small-angle X-ray scattering(SAXS),high resolution transmission electron microscopy(HRTEM),nitrogen adsorption/desorption isotherms,and 29Si magic-angle spinning(MAS)NMR spectroscopy.Optical properties were studied by using UV-vis absorption spectra,UV-vis diffuse reflectance spectra,FT-IR spectra and so on.In the final part of the thesis,a rhodamine B functionalized bis-polydiacetylene(RB/bis-PDA)film sensor was prepared through co-assembly of bis-diacetylene-bridged silsesquioxane(bis-DA)and rhodamine B organosilane followed by topochemical polymerization of bis-DA monomers.Rhodamine B derivatives as the ion-recognition elements were successfully introduced into the bis-polydiacetylene matrix,thus a bis-ratiometric absorbance sensing system for aluminum ions was constructed.The main research contents are as follows:(1)Diacetylene-bridged periodic mesoporous organosilicas(DAPMOs)were synthesized using a cationic trimeric surfactant as the structure-directing agent through the co-condensation of the diacetylene-bridged silsesquioxane(DASi)precursors and tetraethoxy orthosilane(TEOS).On the basis of characterizing the structural properties of the materials,the optical properties of the materials were further studied.The excitation spectrum of DASi shows two absorption bands at 240 and 285 nm ascribed to the π-π*electron transition of conjugated C≡C-C≡C,which is consistent with the UV-vis absorption spectrum of DASi.For those of the hybrid materials DAPMOs,a new peak at 330 nm appears besides the above signal bands.This low-energy band at 330 nm may originate from the formation of aggregates between diacetylene groups,suggesting strong interaction between the diacetylenic groups embedded in the silica framework.Furthermore,using cationic trimeric surfactant and decylviologen as the mixed templates,a charge-transfer(CT)system was constructed,in which diacetylenic groups in the pore walls were as the electron donors and decylviologen molecules as the electron acceptors were locked in the pore channels.The UV-vis diffuse reflectance spectra and soft X-ray absorption near-edge structure(XANES)spectroscopy showed the formation of the CT complex.Importantly,the energy transfer from the diacetylene aggregates to the CT complex occurred upon excitation at 330 nm,which was demonstrated by the fluorescence spectra of the CT systems.(2)Polydiacetylene-based periodic mesoporous organosilicas(PDAPMOs)films with different molar fractions of diacetylene-bridged silsesquioxane(DASi)were synthesized under acidic conditions through the evaporation-induced self-assembly followed by the topochemical polymerization via 254 nm ultraviolet radiation.The as-prepared blue PDAPMOs films are sensitive to temperature,and could undergo a multi-step thermochromic process,turning purple,red and yellow successively under heat stimulation over a wide range from room temperature to above 150 ℃.The high temperature triggered multi-step color transition process could be divided into two stages:the first reversible blue-to-purple-to-red transition and the second irreversible red-to-yellow transition.The purple-to-red transition in the first stage was rapidly and completely reversible,and the reversibility could be repeated for many heating-cooling cycles.The mechanism of the thermochromic response was studied through Raman and temperature-dependent FT-IR spectra,the results of which successfully highlighted the close relationship between chromatic transitions and the conformational changes of PDA backbone.Furthermore,the PDAPMO films could also respond chromatically to mechanical stress and organic solvents,expanding their application in portable sensors.(3)Bis-diacetylene-bridged silsesquioxane(bis-DA)was synthesized with the diisocyanate group as the linking unit.Then a rhodamine B functionalized bis-polydiacetylene(RB/bis-PDA)film was prepared through the evaporation-induced co-assembly of bis-DA and rhodamine B organosilane followed by topochemical polymerization of bis-DA monomers.By considering the requirements of polymerization of diacetylenes and the absorption intensity of ring-opening of the spirolactam-rhodamine derivative,the molar ratio between bis-DA and rhodamine B organosilane was selected as 10:1.Rhodamine B derivatives as the ion-recognition elements were embedded in the bis-polydiacetylene matrix through the hydrolysis/condensation process of organic silicon.The as-prepared blue phase RB/bis-PDA film still retained the thermochromic properties of PDAs,and changed to a yellow phase at high temperature.Both blue and yellow RB/bis-PDA films could be used to selectively identify Al3+.The UV-vis absorption spectrum of the Al3+-containing film showed two separate absorption peaks,corresponding to ring-opening of the spirolactam structure in rhodamine moiety(556 nm)and blue(617 nm)or yellow(470 nm)phase PDAs,respectively.By utilizing the different intensity ratios of the two absorption signals(A556/A617 or A556/A470),the RB/bis-PDA system could be used as a bis-ratiometric absorbance sensor for Al3+.The X-ray absorption near-edge spectroscopy(XANES)analysis was used to study the coordination environment of Al3+ in RB/bis-PDA film,and the result suggested that Al in RB/bis-PDA film may be 6-coordinate.