Syntheses And Properties Of Functional Lanthanide-Containing Ionic Liquids

Ionic liquids have been widely used in organic synthesis, catalysis, functional materialspreparation and many other fields. Lanthanide（Ⅲ） complexes have excellent fluorescenceperformances because of the special electron configurations from lanthanide, and become thenew luminescence materials. The compounds of lanthanide-containing ionic liquids are somespecial ionic liquids which contain multiple performances from lanthanide ions, ionic liquids andliquid crystals. This article reports the soft luminescence materials which can be synthesized byimidazole nitrate ionic liquids, lanthanide ions and a series of ligands, studies their fluorescenceperformances. Specific research contents and conclusions include the following four aspects:1. Five kinds of ionic liquids1-alkyl-3-methylimidazolium nitrate [C_nmim]NO₃（n=2,4,6,8,10; mim=N-methylimidazolium） were synthesized by two steps from N-methylimidazolium,alkyl bromides and sodium nitrate. Their structures were charactered and analyzed by infraredspectra （IR）, ultraviolet spectra（UV）, proton nuclear magnetic resonance （1H NMR）, massspectrometry （MS） and elemental analyses （EA）. Their physico-chemical properties such asthermal decomposition temperature, density, viscosity, dissolubility, water absorbability andelectric conductivity were tested. The test result showed that the decomposition temperature,density, water absorbability and electric conductivity of the ionic liquids were gradually reduced,the viscosity and dissolubility were gradually increased with the growth of the carbon chain.2. Lanthanide-containing ionic liquids [C_nmim][Ln（NO₃）₄]（Ln=Eu, Tb） were prepared byreactions of [C_nmim]NO₃, europium nitrate or terbium nitrate. The structures of[C_nmim][Ln（NO₃）₄] contained1-alkyl-3-methylimidazolium cations and [Ln（NO—3）₄]anions inwhich each lanthanide ion was coordinated with eight oxygen atoms from four nitrate ions werefurther confirmed by ESI mass spectrometry. The photoluminescence properties of thelanthanide-containing ionic liquids were studied at room temperature in water by measuringemission and excitation spectra. These experiments demonstrated that the solution of[C_nmim][Ln（NO₃）₄]（Ln=Eu, Tb） showed strong characteristic fluorescence. Temperature andconcentration influenced the solution fluorescence intensity of [C_nmim][Ln（NO₃）₄]. Due to theintermolecular collision intensified in solution with temperature increasing, the fluorescenceintensity of [C_nmim][Ln（NO₃）₄] decreased. Fluorescence intensity increased with theconcentration increasing, while fluorescence quenching phenomenon appeared when exceeded acertain concentration.3. Thirty kinds of lanthanide-containing ionic liquids [C_nmim][Ln（β-diketone）₃HQ] weresynthesized from [C_nmim]NO₃, β-diketone（TTA=2-thenoyltrifluoroacetone, AcAc=acetylacetone, DBM=dibenzoylmethane）,8-hydroxylquinoline, europium nitrate or terbiumnitrate. Their structures were confirmed by ESI mass spectrometry, the spectra showed thatcations were1-alkyl-3-methylimidazolium, anions were [Ln（β-diketone）₃HQ]—in which eachlanthanide ion was coordinated with six oxygen atoms from three same β-diketone, one oxygenatom and one nitrogen atom from one8-hydroxylquinoline. The fluorescence properties of[C_nmim][Ln（β-diketone）₃HQ] were studied and properties were influenced by β-diketone and8-hydroxylquinoline. β-diketone were main lidands and8-hydroxylquinoline was synergetic ligand. There was matching degree between triplet state energy of β-diketone and the excitedstate energy of lanthanide, the efficiency of energy transfer from ligand to lanthanide wasdetermined by the matching degree, the photoluminescence property was also affected bymatching degree.2-thenoyltrifluoroacetone or dibenzoylmethane matched europium ion whichmade [C_nmim][Eu（TTA）₃HQ] or [C_nmim][Eu（DBM）₃HQ] show red fluorescence,acetylacetone matched terbium ion which made [C_nmim][Tb（AcAc）₃HQ] show greenfluorescence.4.[C_nmim][Ln（DPA）₂]（Ln=Eu, Tb; DPA=2,6-pyridinedicarboxylic acid） were prepared byreactions of [C_nmim]NO₃,2,6-pyridinedicarboxylic acid, europium nitrate or terbium nitrate. Thestructures of compounds showed that cations were1-alkyl-3-methylimidazolium and anionswere [Ln（DPA）₂]—in which each lanthanide ion was coordinated with four oxygen atoms andtwo nitrogen atoms from two2,6-pyridinedicarboxylic acid. The triplet state energy of2,6-pyridinedicarboxylic acid matched the excited state energy of lanthanide,[C_nmim][Eu（DPA）₂]showed red fluorescence,[C_nmim][Tb（DPA）₂] showed green fluorescence.