Syntheses And Studies On Optical Properties Of ?-diketonate Rare Earth Complexes Coordinated With A Stilbene Derivative

Rare earth complexes have been researched for many years,its application prospects mainly cover the fields of catalytic materials,polymer matrices,new drugs development,magnetic materials and fluorescent molecular sensors.Among them,?-diketonate rare earth complexes have unusual spectral characteristics,due to the high absorption coefficient of ?-diketone ligands and effective intramolecular energy transfer to rare earth ions,including sharp emission peaks,small peak widths at half height,long lifetimes,and high fluorescence quantum yields.Therefore,the rare-earth?-diketonate complex with strong luminescence has been widely used in flat panel display materials,luminous probes in bioassays,ultraviolet sensors,and laser materials.Stilbene derivatives have rich optical properties such as reversible photoisomerization,photocyclization,photodimerization and fluorescence.When it is introduced into rare earth complexes,the excited state lifetime of the rare earth complex is affected by the energy transfer of the stilbene derivative ligand.The f-electrons in the inner layer of rare earth ions are less likely to affect the electronic transitions of the ligands,and the coordination of rare earth ions perturbs the electronic transition of the ligand,which can affect the isomerization behavior and energy transfer of the stilbene derivative ligand,it is expected to develop into a dual-functional material with photoisomerization and optical properties.In this article,a novel stilbene derivative ligand N',N'-bis(pyridin-2-ylmethyl)-4-styrylbenzoylhydrazine)(HL)and 2-thienyl trifluoroacetone(Htta)are chosed to coordinated with rare earth ions to obtain the corresponding five rare earth(La,Eu,Gd,Nd,Yb)complexes.We use mass spectroscopy,nuclear magnetic resonance spectroscopy,elemental analysis,infrared spectroscopy,thermogravimetric analysis,X-ray powder diffraction to characterize them.X-ray crystal diffraction is used to determine their crystal structures.We study the photo-cis-trans isomerization behavior of the ligand HL and five complexes in ethanol and acetonitrile solutions.The photoisomerization rate constants and quantum yields can be obtained through the first-order reaction kinetic equation and related formulas.The results show that the photostability of the complexes is better than the ligand.The isomerization rate constant kiso of the complex[Gd(tta)2(HL)(CF3COO)]is the largest,which is 7-8 times higher than the ligand HL.The second is the complex[Eu(tta)2(HL)(CF3COO)],which theisomerization rate constant is 5-6 times higher than the ligand HL.We scaned the fluorescence spectra ofthe complexes[Eu(tta)2(HL)(CF3COO)]?[Nd(tta)2(HL)(CF3COO)]and[Yb(tta)2(L)],of which the complex[Eu(tta)2(HL)(CF3COO)]has the highest fluorescence quantum yield and lifetime.This indicates that the complex[Eu(tta)2(HL)(CF3COO)]is a dual-functional material that has both photoisomerization properties of the stilbene derivative and luminescence properties of the rare earth ion.TD-DFT calculations of ligands were performed,by comparing the energy level difference between the first excited triplet state of ligands and the lowest excited state of the rare earth ions,which explained that the complex[Eu(tta)2(HL)(CF3COO)]has higher fluorescence quantum yield and lifetime,and the complexes[Nd(tta)2(HL)(CF3COO)]and[Yb(tta)2(L)]have low fluorescence quantum yields and lifetimes,and the complex[Gd(tta)2(HL)(CF3COO)]does not luminescence.Finally,the work of the full text is summarized and prospected.