Fabrication And Characterization For Rare Earth Luminescent Lyotropic Liquid Crystals

Rare earth elements are known as "the gold of industry" due to their excellent photophysical properties such as sharp emission lines,large Stokes shift and long(millisecond-order)lifetimes,which arising from their partial filled 4f-shell and high coordination numbers.The introduction of rare earth ions and their complexes into organized molecular aggregates of lyotropic liquid crystals(LLCs),could not only improve their luminescent efficiency and photo-thermal stability,but also endow them better processibility.Consequently,the preparation of functional organized soft materials with both excellent photophysical properties and flexible tunability by virtue of the rich and tailorable phase morphologies of LLCs,as well as their environmental responsiveness should be of great potential.At the same time,the ionic liquid(IL)are regarded as an ideal dispersion medium for rare earth luminescent materials and attractive sovent for organized molecular aggregates.Therefore,design and fabrication of rare earth luminescent soft materials based on ILs will be an efficient way to improve the performance of traditional materials and expand the application of functional organized soft materials,which will be of great significance both in foundmental study and in application fields of rare earth photophysics,supramolecular chemistry,and materials science.In this dissertation,a series of rare earth luminescent LLCs soft materials,especially those based on ILs with tunable phase structure and luminescent properties have fabricated by the introduction of rare earth compounds into organized aggregated structures of LLCs through a convenient self-assembling method.The energy transfer of the rare earth compounds in different LLC phase structures have been systematically investigated by changing the molecular structure and type of the rare earth compounds,amphiphilic molecules and ILs.The main contents of this dissertation include the following four parts:1.LLCs with three phase structures have been constructed by the mixtures of Eu(NO3)3·6H2O and Pluronic P123 amphiphilc block copolymer.The reverse hexagonal,reverse bicontinuous cubic,and lamellar LLC structures could be formed in sequence with the increasing salt proportion.Fourier-transformed infrared spectroscopy(FTIR)measurement demonstrates that the hydrated europium salt could form hydrogen bond between coordinated water molecules and PEO blocks,which plays a key role in the formation of reverse LLCs.The appearance of reverse phase structures can be attributed to the lower affinity of water molecules due to its coordination with europium ions.Analysis of the phase structure and rheological property shows that the luminescence quenching effect of lanthanide ions is efficiently suppressed due to the substitution of coordinated water molecules by oxyethyl groups of P123 and ordered phase structures of LLCs,where the coordinated europium ioins are confined and isolated by PEO blocks.Compared to the solid state and aqueous solution of europium hydrate,the fluorescence quantum yield and lifetime have improved in the reverse LLC phase.2.The europium ?-diketonate complex with 1-butyl-3-methylimidazole ion as counter ion has been synthesized,and the luminescent properties doped in LLCs matrix constructed by P123 and an aprotic IL,1-butyl-3-methylimidazolium hexafluorophosphate([Bmim]PF6)have been investigated.The maintenance of the ordered LLC phase structures after doping with europium complex provides a favorable environment for the well dispersibility of the europium ?-diketonate complex,and also contributes to the extraordinary luminescence property as well as stability of the materials.Compared to the solid state and complex dissoved in the organic solvent,the rare earth complexes confined in ILs-based LLCs matrix,not only maintained the good photostablility in ILs,but also improved the fluorescence performance and stability through the effective confining and shielding by the LLC matrix.The analyses by FTIR measurement shows that stronger hydrogen bonding effect existed in the lamellar phase,which resulted in better energy transfer efficiency and stability.3.The europium ?-diketonate complexes with different substituent chain length of imidazole ion as counter ions have been designed and synthesized,and the luminescence properties in their doped lamellar LLC matrix constructed by sterol amphiphilic molecules BPS-n and[Bmim]PFF6 have been investigated.As a result of the efficiently confining of europium complex within the lamellar LLC matrix constructed by BPS-n,excellent luminescence performence can be obtained.In the lamellar LLCs of BPS-5/[Bmim]PF6,the europium complex exhibits the longest fluorescence lifetime and the higthest quantum efficiency so far reported for the rare earth containing lyotropic organized soft materials.In addition,with the growth of the alkyl chains,the interaction between europium complex and the LLC matrix is weakened,leading to the decreased luminescence properties and photostability of the europium complex.The increase of the oxyethylene chain length in BPS-n will further weaken the orderness of the LLC structure and also the intermolecular interaction of the matrix,which leading to the decrease of the luminescent performance of the europium complexes.4.The europium ?-diketonate complex with ethylammonium ion as counter ion,ethylammonium tetrakis-(thenoyltrifluoro-acetonato)europate(?)(EA[Eu(TTA)4]),has been designed and synthesized,and the luminescence properties doped in LLCs matrix constructed by P123 and a protic IL,ethylammonium nitrate(EAN),have been investigated.Investigation shows that the ethylammonium cation has established a more effective hydrogen bonding interaction with TTA ligand compared to the imidazole ion.For this reason,the coordination structure of the complex is more stable and thus obtained a sizeable elongation of the excited-state lifetime in EA[Eu(TTA)4]complex.Meanwhile,the similar three-dimensional hydrogen bond network within EAN to that of water,not only facilitates a more stable structure of LLC matrix to achieve an excellent photostability,but also endows ILs superior self-assembling capability.Therefore,the fabrication of LLC matrix with richer phase structures like normal micellar cubic,hexagonal,lamellar,and reverse bicontinuous cubic phases can be realized for a relatively wider range of tunable properties for luminescent LLC materials.Through studying the luminescent properties and energy transfer process of europium ?-diketone complexes in different phase structures,the optimum luminescent performance and photostability have been achieved in the reverse bicontinuous cubic phase.