Synthesis And Fluorescence Properties Of Zinc-rare Earth Heteronuclear Metal Complexes

Zn-Ln emissive materials have widespread technology applications,such as those used in bioanalysis,medical imaging,sensors,light emitting diodes,and telecommunications.To pursue highly efficient emission is the constant subject for luminescence materials.However,in NIR-emissive lanthanide complexes,the high energy oscillator,such as C-H,N-H and O-H vibrations in ligands,was the primary factor to quench the luminescence of Ln3+ ion.In order to solve these factors,firstly sandwich-shaped complexes was designed to encapsulate Ln3+ ions in cavity to prevent solvent coordination;Secondly halogenation of ligand is designed to upgrade the quantum yields because of the heavy effect.The details are as follows:1.5-bromosalicylic aldehyde with N,N'-dimethylethylenediamine ligand(H2L1)was selected to react with DBM or TTA to obtain a series of ten complexes[Zn(OAc)(?L1)Ln(DBM)2][Ln=Nd(1),Sm(2),Eu(3),Gd(4),Yb(5)]and[Zn(OAc)(?L1)Ln(TTA)2][Ln=Nd(6),Sm(7),Eu(8),Gd(9),Yb(10)],X-ray crystallographic analysis revealed that the complex exhibited a sandwich structure.Photophysical properties showed complexes 1,2,6,and 7 exhibited fluorescence emission of the characteristic Ln(?)ions,while 4,5,9 and 10 all showed the near-infrared luminescence of the characteristic Ln(?)ions.Moreover the complex 5 showed the excellent NIR luminescence properties with quantum yields reaching 2.22%.2.5-methylsalicylic aldehyde with N,N'-dimethylethylenediamine ligand(H2L2)was selected to react with DBM to obtain a series of five complexes with same structures[Zn(OAc)(?-L2)Ln(DBM)2][Ln=Nd(11),Sm(12),Eu(13),Gd(14),Yb(15)].X-ray crystallographic analysis revealed that the complexes exhibited a sandwich structure.Photophysical properties showed complexes 12 and 13 exhibited fluorescence emission of the characteristic Ln(?)ions,while 11 and 15 showed the near-infrared luminescence of the characteristic Ln(?)ions,and the complex 15 exhabited the NIR luminescence properties with quantum yields reaching 0.50%.The above results showed that the heavy atom effect by halogenated of ligands and the sandwich structure can effectively improve the luminescence quantum yield of Ln(?)complexes.