Properties And Functions Of Fluorescent Assemblies By Synergistic Construction With Amphiphilic Molecules

Self-assembly is a spontaneously process in which building elements assemble into ordered structures through the weak and non-covalent interaction without disturbance of external forces.Amphiphilic molecules are important part in the field of self-assembly and have gradually expanded to the field of supramolecular chemistry.The self-assembly of amphiphilic molecules is playing an increasingly important role in the various interdiscipline subjects due to the diverse construction primitives,simple construction methods,rich responsiveness and functionality.Fluorescence is the unique physical and chemical propertie,which is the process of light emission by absorbs external energy.Because of excellent photoelectric properties,it has been widely used in our basic necessities of life.The development of fluorescent materials has experienced dye molecules,semiconductor quantum dots,lanthanide metal ions,and fluorescent nanomaterials.Simple synthesis methods,flexible controllability and rich functionality have become new directions for the development of fluorescent materials under the premise of ensuring strong fluorescence intensity,long fluorescence lifetime and high quantum yield.In the process of continuous exploration,the research and development of fluorescent assemblies based amphiphilic molecules have greatly expanded the applications of fluorescent materials in life sciences,information sciences,materials sciences,and nanosciences.The fluorescent assemblies can not only retain and improve the fluorescence properties of the fluorescent building element,but also give the flexibility of the assemblies.The structural characteristics of the assemblies can achieve functional and application breakthroughs.Although there have been many researches and reports on fluorescent assemblies,their flexibility and functionality as functional materials still need to be improved,especially their ability to adapt to some special environments.Therefore,developing fluorescent assemblies of synergistic effect with amphiphilic molecules and fluorescent building elements has important scientific significance and application value.This thesis mainly uses the synergistic effect of fluorescent construction primitives and amphiphilic molecules to construct various fluorescent assemblies,such as vesicles,gels and nanoparticles.Their potential applications in fluorescent detection and optoelectronic devices have been developed.In particular,the application scope of fluorescent materials in low temperature environments has been expanded.In Chapter Ⅰ,we describe the current research status of amphiphilic molecular fluorescent assemblies,including main construction strategies,common construction primitives,essential luminescence principles,assembly types,functions and applications.The designing ideas of the fluorescent assemblies of amphiphilic molecules are reviewed in detail,including the co-assembly of amphiphilic molecules(mainly surfactant molecules)with fluorescent building elements and the self-assembly of new fluorescent amphiphilic molecules.The characteristics and advantages of fluorescent assemblies are pointed out.We also raised the problems which still need to be solved.Finally,we summarize the theme,research content and significance in this thesis.In Chapter Ⅱ,the new organic-inorganic hybrid amphiphilic molecule(POM-PPCT)containing polyoxometalate(POM)and the fluorescent building element Eu3+were used to self-assemble in solution to form fluorescent vesicles.We thought that the driving forces of fluorescent vesicles were metal ion coordination andπ-π interaction.Terpyridine molecule possessed excellent photoelectric properties,which could be used as the sensitizing group and induce the photoluminescence properties of Eu3+through the antenna effect.In addition,due to the dynamic properties of the coordination interaction,fluorescent vesicles showed responsiveness to heavy metal ions Cu2+.The fluorescence quenching effect realized the recognition of Cu2+,which had good sensitivity and selectivity.The detection limit was up to 24 nM and could resist the interference of other metal ions,which proved that fluorescent vesicles could be used as an ideal sensing platform for detecting Cu2+.In Chapter Ⅲ,we selected the easily synthesized copper nanoclusters(CuNCs)as the fluorescent building elements,and studied in detail different organic solvents(methanol,ethanol,n-propanol,isopropanol,N,N-dimethylformamide,sulfoxide).CuNCs with glutathione as ligand and stabilizer could self-assemble to form spherical nanoparticles with different sizes driven by different organic solvents.The nanoparticles showed excellent aggregation-induced emission(AIE)characteristics.We proved that AIE characteristic was mainly determined by the volume ratio of the CuNCs aqueous solution to the organic solution,which had good reversible response.At the same time,the tightness of the arrangement of CuNCs in the nanoparticles was different due to the difference in polarity of different organic solvents.Assemblies showed different fluorescence intensities and unlike fluorescence emission wavelengths in the various mixed solution.Hence,the fluorescent assemblies could be used as an effective means to distinguish different organic solvents.In Chapter Ⅳ,to improve the ability of fluorescence detector to resist background interference,we introduced natural amino acid(tryptophan,Trp)into the CuNCs aqueous solution as reference fluorescent chromophore to construct dual emission ratio fluorescent probe,which further improved the sensitivity and accuracy of detection.Two fluorescent chromophores self-assembled to form spherical nanoparticles by multiple hydrogen bonds.The responsiveness of CuNCs to H2O could be used to detect water content in mixed solvents.It was found that this fluorescent probe had two main advantages.Firstly,fluorescent probe had flexible adjustment.The colorimetric range could be adjusted by changing the type of amino acid,amino acid concentration and solvent ratio.Secondly,fluorescent probe had good antifreeze.Freezing point of fluorescent probe was only related to the solvent ratio.The freezing point would change from-45℃ to-4℃ when the solvent ratio was adjusted from 3:7 to 1:9,which could reach the requirements of using in different temperature environments.This fluorescent probe could be used to determine the alcohol content,and we hoped that it could be used as a new type of fluorescent sensing platform applied in real life.In Chapter Ⅴ,CuNCs could also be used as a new type of low molecular weight gelator(LMWGs),which induces the formation of fluorescent gel in the metal ion Zn2+.The structure of fluorescent gel were cross-linking of nanoparticles.The existence of Trp could not only realize the construction of heterogeneous network gel to enhance the fluorescence performance,but also realize the adjustment and inversion of the chiral signal through the superposition of the chiral signals of the two networks.The synergistic effect of solvent and metal ion coordination made the gel have an AIE phenomenon,which gave gels excellent fluorescence performance.The mixed solvent of H2O/DMSO gave the gel excellent frost resistance.The experimental results also showed that the gel exhibit excellent responsiveness to external stimuli(mechanical force,temperature,pH,H2O2,EDTA).Therefore,the sol-gel transition and fluorescence intensity change can be used as judgement standard to realize the identification of different kinds of anions.The gel material not only greatly improved the stability of the fluorescent assemblies based CuNCs,but also provided a new idea and method for the construction of chiral fluorescent materials.In Chapter Ⅵ,the ligand molecules of CuNCs could also give them the ability to further co-assemble.The electrostatic interaction between cationic surfactant and the carboxyl group of the GSH was used to form a new amphiphilic complex,in which CuNCs served as the hydrophilic part and the surfactant tail chain as the hydrophobic part.With the increasing of the surfactant concentration,the structure of the complex changed from polar structure to non-polar structure,which also made the structure of the assemblies change from spherical nanoparticles to network structures.Surfactants could control the fluorescence properties of the assemblies by affecting the hydrophobic interaction and molecular spacing.The fluorescent assemblies could be used as orange phosphor for the construction of light emitting diodes(LEDs).We hoped that this simple and flexible method can provide new ideas and methods for the development of fluorescent solid materials.