双稀土配合物的多路径能量传递与近红外发光性能

Multipath energy transfer and NIR luminescent properties of dual-lanthanide complexes

用乙烯基苄基取代的三脚架配体N,N,N,-三(2-苯并咪唑亚甲基)胺(TVPNTB),与稀土氯化物构筑了一系列单稀土和双稀土配合物,基于配体的天线传能效应,表现出良好的近红外发光性能.其中,在双稀土配合物TVPNTBSmxNd1-xCl3、TVPNTB-SmxYb1-xCl3和TVPNTB-SmxEr1-xCl3中,配体可以同时向两种稀土传能,由此获得的多色带近红外发光使其可以作为潜在的防伪条形码材料.同时,我们探究了两种稀土离子间的传能特性,证实了Sm到Nd、Sm到Yb之间可以产生有效的交叉弛豫能量传递,最大传能效率(η)分别达到39%和36%,并由此分别将Nd和Yb的近红外发光寿命(τ)提高了4倍和2倍;而Sm到Er之间不能产生有效传能.上述多路径传能和敏化发光策略为制备新型、高效近红外发光配合物材料及其应用提供了理论基础.

Near infrared(NIR)-emitting lanthanide ions,especially Sm^3+,Nd^3+,Yb^3+,and Er^3+,show special advantages in nondamage and deep-reaching biological imaging and telecommunication field.But most lanthanide ions have low luminescent efficiency in the NIR region,as a result of insufficient protection of the metal centers against non-radiative deactivation processes and/or inefficient inter-or intramolecular energy transfer.In recent years,organic ligands have been used as antennas to sensitize lanthanide ions to improve their luminescent efficiency.Because the chemical properties of lanthanide ions are very similar,mixed lanthanide complexes can be formed.At the same time,lanthanide ions have many energy levels,the energy transfer is easy to occur between different lanthanide ions.Thus,we can make use of these multipath energy transfers to obtain efficient dual/multi-lanthanide multi-component NIR luminescent materials,which can be used for the ideal multi-channel near-infrared luminescence anti-counterfeiting bar code application.Herein,A series of NIR luminescent mono-or dual-lanthanide complexes were synthesized by TVPNTB ligand with lanthanide chloride salts.The monocrystalline structures of these rare earth complexes were obtained by X-ray single crystal diffraction.These lanthanide complexes are all hetero-isomorphic structures,crystallized in the monoclinic system and belong to P21/c space group.The phase purity was also proved by powder X-ray diffraction(PXRD).For the series of one component lanthanide complexes,the ligand TVPNTB can transfer energy to the excited state energy level of Sm^3+,Nd^3+,Er^3+,Yb^3+,Pr^3+,Dy^3+,and Ho^3+,and produce NIR luminescence of the order of microsecond lifetime.Among them,the NIR luminescence studies of several lanthanide complexes such as Pr^3+,Dy^3+,Er^3+,and Ho^3+are rarely reported.The results showed that the TVPNTB ligand has good near-infrared photosensitization effects on Sm^3+,Nd^3+,Yb^3+,and Er^3+.Moreover,by comparing the energy level difference of these ions,it is found that the energy level difference of Sm^3+from 4G2/5 to 6F5/2 is close to the energy level difference of Yb^3+from 2F5/2 to 2F7/2 in the ground state,and the energy level difference of Nd^3+from 4F3/2 to 4I11/2,which may lead to the cross relaxation energy transfer between rare earth ions and enhance the luminescence of Yb^3+and Nd^3+.So we prepared a series of dual-lanthanide complexes,such as TVPNTBSmxNd1-xCl3,TVPNTB-SmxYb1-xCl3 and TVPNTB-SmxEr1-xCl3.Energy transfer from the antenna ligand can sensitize both NIR luminescence of the two lanthanide ions,which might serve as NIR polychromatic anti-counterfeiting luminescent barcode materials.We also investigated the energy transfer properties between the dual lanthanide ions,and confirmed that crossing relax energy transfer from Sm^3+to Nd^3+,or from Sm^3+to Yb^3+were realized.The largest energy transfer efficiency(η)reaches 39%and 36%,leading to 4 or 2 times longer of the decay lifetimes of Nd^3+and Yb^3+,respectively.Through the study of NIR luminescence performance of dual-lanthanide complexes with different proportions,it is clear that in addition to the antenna energy transfer from ligand to lanthanide ions,there is also a crossrelaxation energy transfer process from Sm^3+to Nd^3+and Sm^3+to Yb^3+,thus achieving the effective energy transfer between dual-lanthanide complexes,thus further improving the NIR luminescence life of Nb^3+and Yb^3+.The multi-path energy transfer strategy summarized in this study not only provides a basis for the preparation of novel high-performance NIR luminescent rare earth complexes,but also provides a reference for the design and synthesis of other multifunctional composite optical materials.