Design,Synthesis And As Fluorescent Sensor Of Lanthanide Complexes

Lanthanide complexes are favored by researchers due to their diverse structures and unique fluorescence properties.In particular,the ligand with"antenna effect"in the lanthanide complex can absorb the energy of ultraviolet light,and then transfer to the central lanthanide metal ion to emit characteristic fluorescence.Moreover,the characteristic fluorescence emitted by the lanthanide complexes is easily affected by the external environment,making the fluorescence quench,enhance or weaken.Because of this,it can be used as a good fluorescent sensing material.On the other hand,the sensitivity of fluorescence sensing is related to its own fluorescence quantum yield.However,most of the reported lanthanide complexes’fluorescence quantum yield is less than 50%,which greatly limits the further development of lanthanide complexes’fluorescence sensing.In this paper,we designed and synthesized a series of new lanthanide complexes with high fluorescence quantum yield to study their performance in detecting metal ions and amino acids in water,and further developed these fluorescent sensors from single-function to dual-function and even three-function fluorescent sensors.The system reveals the fluorescence sensing mechanism of lanthanide complexes.（1）Highly luminescent lanthanide complexes constructed by bis-tridentate ligand and as sensor for Et₂OMono-nuclear lanthanide complexes[Ln（tppz）（acac）（NO₃）₂]·acac(tppz=2,3,5,6-tetra-2-pyridinylpyrazine;acac=acetylacetone;Ln³⁺=Tb³⁺,1a;Er³⁺,1b;Y³⁺,1c)are obtained by introducing the bis-tridentate ligand tppz for the first time.These complexes are fully characterized and luminescence properties are investigated in detail.It is interesting to find that 1a has highly luminescent quantum yield of 69%.Further investigation revealed 1a is a sensitive probe to detect Et₂O.（2）Highly luminescent Ln-MOFs based on 1,3-Adamantanediacetic acid as bifunctional sensorA series of lanthanide metal-organic-frameworks（Ln-MOFs）are synthesized under mild hydrothermal conditions by introducing the ligand of 1,3-adamantanediacetic acid（H₂ADA）.They are three dimentional（3D）structures and with the formula of[Ln（ADA）_1.5（phen）]_n(Ln³⁺=Eu³⁺,2a;Gd³⁺,2b;Tb³⁺,2c;La³⁺,2d;Ce³⁺,2e;Pr³⁺,2f;Nd³⁺,2g;Y³⁺,2h;phen=1,10-phenanthroline).These Ln-MOFs are fully characterized by single-crystal X-ray diffraction,PXRD,TGA,EA and FT-IR.Luminescence properties,including luminescence spectra,luminescence decay lifetimes and luminescence quantum yields（QYs）are analyzed in detail.Eu³⁺complex of 2a shows highly luminescence QYs of 58.61%,which due to that the triplet state of phen competes well with the excited emission state of Eu³⁺.Further investigation reveals that 2a is a bifunctional sensor,which can be used as a turn-off luminescence sensor for Ni²⁺and turn-on luminescence sensor for Val at the same time.Interestingly,the limit of detect（LOD）for sensing Ni²⁺is an ultrahigh sensitive value of 1.0×10^-9 M(5.9×10^-5 mg/L),which is lower than the Chinese environmental quality standard(0.5 mg/L of total Ni²⁺content,GB25467-2010),and it is the most sensitive chemosensor for detecting Ni²⁺,to the best of our knowledge.Investigation also reveals there is a good linear relationship between luminescence intensity and the Ni²⁺concentration in 0.2-0.6μM.The sensing mechanism for Ni²⁺and Val are also discussed.（3）Ultrahigh luminescence quantum yield lanthanide coordination polymer as multifunctional sensorInvestigation and development of advanced multifunctional and sensitive sensors with high luminescent quantum yield and capabilities of detecting different analytes such as metal ions are imperative.Due to their inherent sup lanthanide coordination complex is one candidate for sensing application,particularly for the multifunctional sensors.Herein,we present two series of alkali ions decorated lanthanide coordination polymers（Ln-CPs）,which show ultrahigh luminescence quantum yields（QYs）of77%（3a）and 92%（4a）.To the best of our knowledge,3a represents the first trifunctional lanthanide complex sensor that can simultaneous detect and discriminate three different analytes,namely H⁺/Cd²⁺/Cr³⁺through multimode optical response.Furthermore,the limit of detection（LOD）for Cr³⁺is an ultralow value of 2.0×10^-9 M with sensing time of 2 h,which is comparable to the most sensitive Cr³⁺chemo-sensor.More interestingly,92%（4a）is the unprecedented luminescence QYs among the reported lanthanide coordination complexes.