Synthesis Of Lanthanide Complexes With Stilbene Derivative And Theoretical Study Of Their Optical Properties

Stilbene derivatives have rich optical properties such as reversible photoisomerization,photocyclization,photodimerization and fluorescence.It has important application prospects in optical functional materials.In recent years,the isomerization of stilbene groups has been coupled to metal complexes(mainly Ru,Ir).During the coupling process,metal ions not only can retain or promote the photoisomerization properties of stilbene derivatives but also endow them with bio-optical and electrical properties.There has been no report about Ln(?)complex with stilbene derivative.The idea about coupling of lanthanide complexes with stilbene derivatives is to introduce the functional groups of stilbene into lanthanide complexes and combine the cis-trans isomerization of stilbene with the f-f electron transition of rare earth.The coordination of rare earth ions involves the electronic transition of the perturbation ligand affects the isomerization and energy transfer of the ligand.In addition,the excited state behavior of lanthanide complexes regulated by energy transfer of stilbene ligand will affect their fluorescent properties,thus the lanthanide complexes developing into a kind of bifunctional molecular-based material.We designed and synthesized a novel series of lanthanide complexes,corresponding to five rare earth elements(La,Eu,Gd,Nd,Yb),that combining stilbene derivative of N',N'-bis(pyridin-2-ylmethyl)-4-styrylbenzoyl hydrazide(HL)and benzoyltrifluoroacetone(tfd).The target was characterized by MS,'H NMR and I"F NMR,FT-IR,TGA,elemental analysis and X-ray powder diffraction.The crystal structure was measured by X-ray crystal diffraction.Subsequently,the photoinduced cis-trans isomerization behavior of ligand HL and five complexes in ethanol and acetonitrile solution was discussed,and the photoisomerization rate constant and quantum yield were obtained by the first-order reaction kinetic equation.The results show that the photostability of the complexes is better than that of the ligand HL,and the isomerization rate constant kiso of the complex[Gd(tfd)2HL.CF3COO]is 3-5 times that of the ligand HL.At the same time,the fluorescence spectra of complexes[Eu(tfd)2HL,CF3COO],[Nd(tfd)2HL·CF3COO]and[Yb(tfd)2.L]were measured at ambient temperature.We found that the complex[Eu(tfd)2HL·CF3COO]have high fluorescence quantum yield and a long fluorescence lifetime.In summary,it can be explained that the complexes[Eu(tfd)2HL.CF3COO],[Nd(tfd)2HL CF3COO]and[Yb(tfd)2*L]are bifunctional complexes,which have both photoisomerization properties of stilbene and fluorescent properties of rare earth ions.Based on the results of TD-DFT calculation of ligands and complexes,by analyzing the main characteristic transitions of the electron absorption spectra in acetonitrile solution,we discussed and explained the photoisomerization phenomena of ligand HL and complexes,including the reason why the cis-trans isomerization yield of complex[Gd(tfd)2HL·CF3COO]reached 5 times of the ligand HL.We analyzed the matching degree between the triplet state energy of the ligand and the excitated state energy of rare earth ions Eu3+,Nd3+,Yb3+and Gd3+.The results not only explain that the fluorescence quantum yield of the complex[Eu(tfd)2HL·CF3COO]is ten times higher than that of its isomorphous azobenzene Eu(?)complex,but also explain the lower fluorescence yield of the complexes[Nd(tfd)2HL CF3COO]and[Yb(tfd)2 L],and the reason why the complex[Gd(tfd)2HL·CF3COO]cannot fluoresce.