Fabrication And Characterization For Novel Luminescent Aggregates Based On Lanthanide Complexes And Ionic Liquids

As an important class of functional metals,rare earth elements have excellent photophysical properties due to their unique 4f electronic layer structure,such as high color purity,large stokes shift,long excited state lifetimes,and rich electronic energy levels,basically covering the whole category of solid light emission,it has been widely used in fluorescent probes,medical radiation and chemical sensors.However,the f-f electron transition of lanthanide ions is forbidden transition,which results in unsatisfactory luminescence of a single lanthanide ion;furthermore,the high sensitivity to water environment and concentration leads to defects such as weak absorption in the visible and ultraviolet regions,poor self-luminous efficiency,and susceptible to quenching effect.The lanthanide complexes used to improve these defects also have the problems of unstable performance and poor ductility,but ordered molecular aggregates can effectively improve the luminescence performance and stability due to strong intermolecular interactions.Meanwhile,ionic liquids have also attracted more attention for the assembly of ordered molecular aggregates.The aggregates constructed in ionic liquids not only have better thermal stability than water or organic solvent systems,but also the flexible and variable molecular structure based on ionic liquids is more conducive to the reversible regulation of aggregate structure and the construction of new aggregation phases.In addition,ionic liquids are also ideal dispersing solvents for lanthanide-containing luminophores,which have the advantages of weak coordination and no interference in the visible and near infrared spectral regions.Therefore,the design and construction of lanthanide luminescent ordered molecular aggregates based on ionic liquids will overcome the shortcomings of traditional luminescent materials,construct lanthanide luminescent soft materials with excellent luminescence performance and controllability,and further expand the functional application of lanthanide luminescent materials,it has important theoretical significance and practical application value to promote the development of interdisciplinary fields such as supramolecular chemistry,lanthanide photophysical chemistry,materials chemistry,physics and biology chemistry.In this dissertation,through self-assembly strategies,using europium complexes with different ligands as the main research subject,a variety of lanthanide luminescent ordered molecular aggregates have been successfully constructed in ionic liquids.The effects of different aggregate structures on the luminescence properties of lanthanide in the same system were compared;the use of a single lanthanide complex to achieve controllable adjustment of multicolor luminescent lyotropic liquid crystals under ultraviolet stimulation;the mechanism of forming self-assembled aggregates directly in ionic liquids by using novel amphiphilic lanthanide complex without the addition of amphiphilic molecular and its effect on energy transfer was discussed.By systematically studying the effect of the structure of ordered molecular aggregates on the luminescence properties of lanthanide complexes,exploring ways to effectively enhance their photophysical properties,a series of new functional lanthanide soft materials with excellent properties and rich phase states were constructed.The contents of this dissertation include the following four parts:In chapter one,based on the basic conception of rare earth elements,the characteristics,luminescence mechanism and research significance of rare earth elements have been summarized,then we outlined the research status of lanthanide luminescent materials.The concept,characteristics and performance of ionic liquids have been summarized,and the self-assembly of amphiphilic molecules to form ordered molecular aggregates were introduced,including the theory of aggregate formation and several important aggregates designed in this dissertation,which focused on the introduction of ionic liquids in the formation of aggregates.We presented the research status of lanthanide luminescent ordered molecular aggregates,including the main lanthanide luminescent aggregates in conventional solvents and ionic liquids.The construction and performance of lanthanide luminescent materials with ionic liquids were summarized.Finally,we presented the main research content and significance of the work.In chapter two,the europium ?-diketonate complex with 1-dodecyl-3-methylimidazole ion as counter ion has been synthesized,then the europium complex co-assembled with the corresponding amphiphilie,1-dodecyl-3-methylimidazolium bromide([C12mim]Br),in a protic ionic liquid,ethylammonium nitrate(EAN),to form luminescent vesicles and lyotropic liquid crystals.Studies have shown that the same imidazole ion[C12mim]+was selected as the cation for the complex and amphiphilic molecules,both not only can be co-assembled in a solvent,thereby increasing its solubility and orderly arrangement,but also the vesicles and LLCs provided a favorable environment for the binding of the complex in the aggregates,so that the complex showed enhanced light-emitting performance and stability in the aggregates.Meanwhile,through infrared spectroscopy,it was found that compared with the vesicle structure,due to the tighter packing and stronger hydrogen bonding interactions,the complexes were more effectively bound and stabilized in the LLC,and showed the best luminescence and stability.This system provided a theoretical reference for the luminescence and energy transfer mechanism of lanthanide complexes in different ordered aggregates.In chapter three,lanthanide complexes with dibenzoylmethane(DBM)and 2,2'-biquinoline(BQ)as ligands were doped with the LLC constructed by[C12mim]Br and protonic ionic liquid EAN.Compared with the complex in the EAN solution,the obtained LLC has enhanced fluorescence intensity and lifetime.Meanwhile,under ultraviolet light for different times,it was the first time to construct a ultraviolet-responsive multicolor fluorescent soft material.The study found that with the prolonged exposure time in ultraviolet light,although the DBM ligand still showed typical photodegradation,but the luminescent intensity of BQ increased significantly due to cis-trans isomerization,so the color of the LLC gradually changed from the initial red light emission to green.This work provided a reference value for the UV-induced photochromism mechanism and the convenient preparation of multicolor fluorescent soft materials.In chapter four,an amphiphilic europium complex with hydrophilic ethoxy chain-modified terpyridine as a ligand was designed and synthesized,and its fluorescence properties in aggregates constructed by self-assembly in different solvents were studied.Multilayer vesicles or spherical micelles were observed in ethanol/water mixed solvent or EAN,respectively.The preparation of self-assembled vesicles from a single amphiphilic lanthanide complex directly in imidazole ionic liquid[Bmim]PF6 were achieved.Compared with the aggregates formed in other solvents,due to effectively shielding of the quenching effects caused by both solvent and complex concentration,the vesicles obtained in[Bmim]PF6 showed the best fluorescence performance and exhibited the potential for fluorescence detection of water molecules.In this work,the preparation of fluorescent aggregates in ionic liquids directly from amphiphilic complexes expanded the effective way of preparing lanthanide luminescent aggregates.