| By virtue of their special optical,electrical and magnetic properties,lanthanide complexes are widely used in many fields,including light-emitting diodes(LED),magnetic resonance imaging(MRI),optical communication,medical diagnosis,optical fiber and so on.Due to their forbidden Laporte rule,introducing sensitizers with high extinction coefficient through antenna effect for highly efficient lanthanide luminescence is necessary.Due to the incompletely overlap spectra between the emission band of the sensitizer and the absorption profile of the sensitized lanthanide,dual emissions including residual emission from sensitizer and the lighting up lanthanide luminescence appear in one lanthanide complex under the same irradiation.Especially,heteronuclear lanthanide complexes,in which one matching energy levels of lanthanide subunit as sensitizer for the other one,is more attractive in both multiple emissions and up-conversion luminescence(UCL),promising in barcoded materials,multiple signal detection,bioimaging probes,and so on.Despite of great progress in lanthanide chemistry in recent years,there is still continuing interest in designing and preparing lanthanide complexes with desired performance based on the well-established structure-property relationship.Because of the similar coordination preferences together with a smooth and monotonic contraction from La to Lu(from 1.216 to1.032(?)),it is very challenging to selectively synthesis and characterize complexes containing two or more lanthanide ions.Herein,the structure and luminescence properties of lanthanide complexes were firstly regulated by organic phosphine oxide ligands with different conjugation but the same length,as both bridging linkers and photosensitizers.Then,the multi-coordination mode of the organic ligand in the lanthanide precursor with further coordinate ability can be used to rationally assemble different lanthanide blocks for discrete heteronuclear lanthanide complexes.Since the antenna effect improve the absorption cross section of the emitting lanthanide ions,enhanced NIR emission and efficient UCL under mild conditions could be achieved as following:The first chapter is the preface,which briefly describes the research progress,current situation and development trend of dual emissive lanthanide complexes,and analyses the novelty,bottleneck and possible solutions based on the research accumulation of our group in lanthanide luminescence.The second chapter is about the regulation of emission spectrum containing residual emission of photosensitizer and luminescence of the sensitized Ln3+.It was found that the conjugation of the bridging bis(diphenylphosphine oxide)alkane or arene ligands can react with Sm(hfac)3(H2O)2(hfac-=hexafluoroacetylacetonato),which controls the structural dimensionality and the emission color of the complexes while retaining the SmIII???Sm IIIdistance constant.Based on the above reaction,reacting lanthanide subunit with bis(diphenylphosphine oxide)-1,4-butane(L1)affords red color and one-dimensional(1D)ribbon{Sm(hfac)3(L1)}n(1),while bis(diphenyl-phosphinoyl)-1,4-benzene(L2)results in near-white emission and two-dimensional(2D)network{Sm(hfac)2(CF3COO)(L2)3}n(2),but bis(diphenyl-phosphinoyl)-9,10-anthracene(L3)forms green and zero-dimensional(0D)cyclic{Sm(hfac)3(L3)}2(3).Thus,it is practical to modulate both the structural configuration from one-dimensional chain to two-dimensional network and even to the zero-dimensional ring,and regulate their emission colors from red to white and further to green,by organic conjugation between SmIII at fixed distance.The third chapter is about the directional construction of heteronuclear lanthanide complexes and regulation of their luminescent performance.This chapter is divided into two sections,one is about the enhanced near infrared(NIR)emission of Ln3+;the other one is about the up-conversion luminescence(UCL)under normal temperature and low power excitation in conventional organic solvents.We assembled YbIII and ErIII in close proximity by the chelating-bridging coordination mode of hydroxide radical from tridentate ligand H2hmq(8-hydroxy-2-hydroxymethylquinoline,L4),to obtain heteronuclear lanthanide complexes{[Yb2Er]2[Er]2}(4,{[Yb2Er(Hhmq)3(CH3COO)3(hfac)2]2[Er(hfac)3(CH3COO)(CH3OH)]2})and{[Er2Yb]2[Yb]2}(5,{[Er2Yb(Hhmq)3(CH3COO)3(hfac)2]2[Yb(hfac)3(CH3COO)(CH3OH)]2})with high coordination numbers(8 and 9),where YbIII with a larger absorption cross-section than ErIII as sensitizer transfers energy to ErIII,and thus when YbIII is directly excited,dual emission from Yb3+and Er3+is exhibited.Further the nonradiative process is effectively reduced through O-H???F hydrogen bond formed by the introduced fluoride and the unprotonated ligand,which induces enhanced NIR dual emissions.Surprisingly,after the introduction of F-into 4 and 5,the two also exhibited the characteristic UCL of Er3+under the excitation of 980 nm laser.It is the improved absorption cross-section of ErIII by YbIII sensitizers,and short distance between YbIII/ErIII(<4(?))that promotes efficient energy transfer of YbIII?Er III,also the introduction of F-that effectively reduces the non-radiative process,result 4 exhibiting UCL with efficiency up to 1.1%??UC?2.3%in organic different solvents under low excitation power density(2 W/cm2)at room temperature,which is the highest one till reported in discrete molecular system.The Higher?UC and longer decay lifetimes of ErIII in 4 than those in 5 under the same conditions,confirm numerous sensitizers for a few emitters promoting the UCL performance.It provides a new strategy for synthesizing discrete f–f bimetallic assemblies under mild conditions for UCL. |
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