Preparation And Property Manipulation Of Luminescent Ordered Aggregates Based On Supramolecular Self-assembly Strategy

Supramolecular self-assembly based on the noncovalent interaction of molecules(electrostatic interaction,host-guest interaction,π-π interaction,H-bonding interaction)is a powerful method for the preparation of functional ordered aggregates.At present,supramolecular chemistry has been intertwined with biological sciences,materials sciences,physical sciences,and environmental sciences,becoming an important method of new functional materials in the 21st century.Luminescent materials have a wide range of applications in optoelectronic devices,biological probes,and molecular sensing.In particular,a novel luminescent material having aggregation induced emmision(AIE)properties overcomes the fluorescence quenching property of traditional luminescent materials in aggregated state,and greatly expands the application of luminescent materials in solid films,phosphors,et al.Herein,we studied the supramolecular self-assembly behaviors of three kinds of AIE molecules:Ag nanoculsters,surfactant with π-conjugated structures and dyes.And studied the application of ordered aggregates.The contents of this paper are as follows:In Chapter Ⅰ,we introduced the background of supramolecular self-assembly,especially,the supramolecular self-assembly behavior based on electrostatic interaction and host-guest interaction.The common types of ordered aggregates,especially vesicles and gel aggregates,are introduced.the development of AIE and the mechanism of the AIE phenomenon are reviewed,especially the molecules withπ-conjugated structures and metal nanoclusters are presented.Finally,the research content and significance of this research are reviewed.In Chapter Ⅱ,we report the controlled self-assembly of the hexanuclear silver nanocluster(Ag6-NCs).Ag6-NCs perform a good solubility in water and can not aggregates in water.So we changed the polarity of solvents trying to induce Ag6-NCs aggregates.It can be found that Ag6-NCs can self-assembly into robust multilayer vesicles in other solvents,DMSO,CH3CN,EG and MeOH.Their unique luminescence endow them with bifunctional probes to sense Fe3+ and DL-dithiothreitol(DTT).By protonating the Ag6-NCs to Ag6-H-NCs using hydrochloric acid(HCl),the multilayer vesicles survived in aprotic solvents,DMSO and CH3CN,but are transformed to nanowires in protic solvents,water,EG and MeOH.Our results demonstrated that the solvent-bridged H-bond plays a key role in the evolution of the morphologies from vesicles to nanowires.Moreover,the nanowires could further hierarchically self-assemble in water into hydrogel with high water content(99.5%),and with remarkable mechanical strength and self-healing properties.This study introduces a robust cluster-based building block in supramolecular self-assembly system and reveals the significance of aprotic and protic solvents for the modulation of the morphologies of cluster-based aggregates.In Chapter Ⅲ,facile supramolecular self-assembly strategy was carried out to enhance the luminescence of Ag6-NCs through multiple electrostatic interactions with polyethyleneimine(PEI).Functional colloid aggregates of Ag6-NCs such as nanospheres and nanovesicles were formed along with the enhanced emission due to the formation of compact ordered self-assemblies,which effectively restrict intramolecular vibration(RIV)of the capping ligands on Ag6-NCs to diminish the non-radiative decay.All those could block energy loss and facilitated the radiative relaxation of excited states which ultimately induced an aggregation induced emission(AIE)phenomenon.Furthermore,the luminescent Ag6-NCs/PEI nanovesicles are pH-responsive and show a superior fluorescent sensing behavior for the detection of Al3+with a limit of detection(LOD)low to 3μM.This work sheds light on the controlled NCs-based supramolecular self-assembly and the NCs-based functional materials which will be well-established candidates in controllable drug delivery,biomarker and sensors in aqueous solution.In Chapter Ⅳ,Fluorescent supramolecular hydrogel was prepared by α-cyclodextrin(a-CD)and Tyloxapol,which can be considered as an oligomer of the nonionic surfactant polyoxyethylene tert-octylphenyl ether(Triton X-100,TX-100)with a polymerization degree below 7.For comparsion,both Tyloxapol and TX-100 were selected to form hydrogels with a-CD to get more information about the interaction between different types of surfactants and cyclodextrin.These hydrogels have been thoroughly characterized by using various techniques including phase behavior observation,transmission electron microscopy,field emission scanning electron microscopy,fluorescence spectra,fluorescence microscopy observations,Fourier transform infrared spectroscopy,1H NMR and rheological measurements.The hydrogels of a-CD/Tyloxapol are responsive to external stimuli including temperature,pH and guest molecules,and present gelation-induced quenching fluorescence emission property.The reason for this phenomenon may be that Tyloxapol molecules come into the cavity of a-CD and form the inclusion complexes.Due to the high electron density of the narrow cavity of α-CD,it induces the shift of the electron on the benzene ring which can weaken the π-π interaction and lead to the fluorescence quenching.Moreover,the hydrogel formed by a-CD/Tyloxapol is highly responsive the formaldehyde(HCHO).Addition of a small amount of HCHO can induce a gel-to-sol transition.Interestingly,once the gel transforms to solution,it becomes fluorescent.This makes a-CD/Tyloxapol hydrogel a promising candidate for HCHO detection and removal in home furnishings to reduce indoor environmental pollutants.In Chapter V,Giant vesicles(1-10 μm)were constructed via a facile ionic self-assembly(ISA)strategy using an anionic dye and oppositely charged surfactant.We further study the property of giant vesicles.(1)Anionic dye Acid Orange Ⅱ(AO)and an oppositely charged cationic surfactant 1-tetradecyl-3-methylimidazolium bromide(C14mimBr)was used to prepare giant vesicle.This is the first report about preparing giant vesicles through ISA strategy.Interestingly,the giant vesicle could keep the original morphology while the solvent was evaporated and displayed solid-like properties at low concentration.Moreover,giant vesicles with large internal capacity volume and good stability in solution could also be achieved by increasing the concentrations of AO and C14mimBr which contributed to the increase of the other noncovalent cooperative interactions.In order to facilitate comparison,a series of parallel experiments with similar materials were carried out to investigate and verify the driving forces for the formation of these kinds of giant vesicles by changing the hydrophobic moieties or the head groups of the surfactants.It is concluded that the electrostatic interaction,hydrophobic effect and π-π stacking interaction play key roles in this self-assembly process.Importantly,the giant vesicles can act as a smart microcarrier to load and release CQD under control.Besides,the giant vesicles could also be applied as a microrector to synthesize monodispersed Ag nanoparticles with diameter of about 5-10 nm which performed a good catalytic capacity.Therefore,it is indicated that our AO/C14mimBr assemblies hold promising applications in the areas of microencapsulation,catalyst support and lightweight composites owing to their huge sizes and large microcavities.(2)Giant vesicle was also prepared by using an anionic dye methyl orange(MO)and C14mimBr on the base of ISA strategy.The properties of MO/C14mimBr complexes were characterized by transmission electron microscopy,field emission scanning electron microscopy and confocal laser scanning microscope,fluorescence spectra and UV-vis spectroscopy.The results indicated that the giant vesicle was formed by the fusion of small vesicles and could keep its original structure during the evaporation of solvent.Besides,the giant vesicles perform luminescent property owing to the break of intermolecular π-π stacking of MO,which suppress the aggregation-caused quenching(ACQ)of dyes.Moreover,MO/C14mimBr complexes also performs smart pH-responsive characteristics,that is,various fluorescent structures(polyhedron-like structure,giant vesicle,chrysanthemum-like structure,peony-like structure)were obtained when pH≥4,while simple nonfluorescent structure(microflake)was obtained when pH=2 due to the changes of MO configuration.Thus,the morphologies and fluorescence intensities could be regulated reversibly by changing the pH,and the fluorescence behavior can be predicted with the color change directly visible to the naked eye.Furthermore,the solid-like giant vesicle also performs abundant thermic phase behavior,which could form thermotropic liquid crystalline phases in a certain scope of temperature.It is expected that the facile and innovative design of supramolecular material by ISA strategy could be used as cargo carrier,pH detection probes,organic conducting materials,and cellular processes mimicry.