三唑类离子型铱配合物的合成、晶体结构及光物理性能研究

Synthesis, Crystal Structure and Photophysical Properties of Ionic Triazole Iridium Complexes

选用5-(4-氟苯基)-1,3-二甲基-1H-1,2,4-三唑(fdpt)作为主配体,分别以4,4’-二叔丁基-2,2’-联吡啶(dtbpy)、2,2’-联吡啶(bpy)和4,4’-二溴-2,2’-联吡啶(dibbpy)为辅助配体,设计合成出3种新型离子型铱(Ⅲ)配合物[Ir(fdpt)2(dtbbpy)]+PF6-(W1),[Ir(fdpt)2(bpy)]+PF6-(W2)和[Ir(fdpt)2(dibbpy)]+PF6-(W3)。通过元素分析、质谱、核磁共振谱、红外光谱和X射线单晶衍射表征了配合物的组成和化学结构,通过紫外可见光谱和光致发光光谱研究了配合物的光物理性能,并同时对比分析了配合物的光稳定性与热稳定性。结果表明,配合物W1,W2和W3均具有较好的光稳定性与热稳定性,其最大发射波长分别为505,520和560 nm,发光颜色由蓝绿色-绿色-黄绿色变化。

The limitations of some traditional transition-metal complex phosphorescent materials had stimulated the exploitation of phosphorescent materials with iridium atom as the center.Iridium complex phosphorescent materials can be divided into neutral iridium complexes and ionic iridium complexes,and early work was focused on neutral types.With the development of correlative research,ionic iridium complexes gained more and more momentum recently,due to having a much simpler synthetic method,reacting from a lower temperature,just needing simple purification processes,and requiring less cost than the neutral type.Ionic iridium complexes combination of cation iridium complex and a kind of counterion,for instance,BF_(4)^(-)or PF_(6)^(-).Among these,the complex part consisted of two cyclometalating ligands (C^(N)),an ancillary ligand (LX),and a center iridium atom.And the highest occupied molecular orbital (HOMO) was in the cyclometalated (C^(N)) ligands involved the lowest excited triplet state energy emission of the complex,whereas the lowest unoccupied molecular orbital (LUMO) was usually located on the neutral (N^N) ancillary ligand.Because the HOMO and LUMO orbitals were normally located on different ligands,the energy gap can be adjusted on the two kinds of ligands independently,or on both of them.These unique structural characteristics of ionic types led to the high emission quantum efficiencies of almost any color,and were endowed with favorable photochemical stability.Therefore,much research showed that the luminous color and wavelength effect of the iridium(Ⅲ)phosphorescent complex had a close relationship with the structures of organic ligands.By modifying the organic ligand frame around the central metal ion,the emission color of the complexes can be controlled by the whole visible range,which means the structure-activity relationship plays a significant role in designing new Iridium(Ⅲ)complex.Three new ionic iridium(III) complexes,[Ir(fdpt)_(2)(dtbbpy)]~+PF_(6)~-(W1),[Ir(fdpt)_(2)(bpy)]~+PF_(6)~-(W2) and[Ir(fdpt)_(2)(dibbpy)]~+PF_(6)~-(W3),were designed and synthesized by using 5-(4-fluorophenyl)-1,3-dimethyl-1H-1,2,4-triazole (fdpt) as the cyclometalated ligand,and4,4'-di-tert-butyl-2,2'-bipyridine (dtbbpy),2,2'-bipyridine (bpy) and 4,4'-dibromo-2,2'-bipyridine (dibbpy) as auxiliary ligands.Among these,fdpt was a new triazole derivative,and triazole was a kind of five-membered nitrogen-containing heterocyclic compound rich inπelectrons,showing an electronic structure similar to pyridine.And phenyl-triazole had higher LUMO energy level and stronger coordination ability,and the fluorine atom on phenyl showed the electron pulling effect onπconjugated system,improved the electronic mobility andf stability of the complex.Besides,about auxiliary ligands,the tert-butyl group in dtbpy belonged to the electrondonating group,and the bromyl group in W3 auxiliary ligands was the electron-withdrawing group.The discrepancy of these auxiliary ligands on substituent groups led to the difference of chemical characterizes,photophysical properties,photostability and thermostability on the three complexes.The compositions and chemical structures of the complexes were characterized by elemental analysis,mass spectrometry,nuclear magnetic resonance spectroscopy,infrared spectroscopy,and single-crystal X-ray diffraction.The structure representation result showed that the central iridium atom was surrounded by C and N atoms of the cyclic metaled ligand and bidentate auxiliary ligand,and the whole molecule presented a hexacoordinated octahedral geometry.The angle parameters indicated that the geometry of this six-coordination had a large distortion with respect to the ortho-octahedron,which was actually a distorted octahedral configuration.Besides,the ability of substituents to gain and lose electrons affected the electron clouds around the iridium atom,which led to the difference of distance between ligands and metal ions.So,from the parameters of these bond lengths,auxiliary ligand dtbbpy had the closest distance from the center atom because of the effect of electron-donating by the tert-butyl group,and the high electronegativity of bromine atoms reduced the electron cloud density of Ir-N coordination bonds and increased the distance between auxiliary ligands and central atoms.The photophysical properties and photostability of the complexes were investigated by ultraviolet(UV)-visible spectroscopy and photoluminescence spectroscopy,and the thermal stability of the complexes was tested by thermogravimetric analysis.In the ultraviolet absorption spectrum,it could be seen that three ionic complexes with the same main ligand have similar absorption properties,and the curve trend accorded with the absorption spectrum characteristics of typical cationic iridium complexes.The photoluminescence spectroscopy results showed that the maximum emission wavelengths of W1,W2 and W3 were 505,520 and560 nm,the colors changed from blue-green,green and yellow-greenish.The results showed that the maximum wavelength of W1 was blue-shifted by 15 nm compared with the emission peak of W2,which indicated that the introduction of large-space electron donor group tert-butyl into the auxiliary ligand could expand the conjugatedπbond system,increase the energy gap,shorten the wavelength and blueshift the emission peak.Compared with W2,the emission peak of W3 shifted to 40 nm,which indicated that the introduction of bromine atom,the pull-up electron group of the auxiliary ligand,changed the charge density distribution of the complex,increased the electron cloud density of the auxiliary ligand,reduced the emission energy level and the energy gap,widened the emission band and redshifted the emission peak.The light stability results showed that with the increase of time,the luminous intensity of the three materials all showed a downward trend,indicating that the quenching phenomenon appeared.Compared with the change of photoluminescence(PL) intensity under shading conditions,it can be seen that under natural light conditions,the luminescent intensity of the complex was greatly reduced,and the intensity of complex W3 was obviously reduced,which was due to the heavy atom effect of bromine,which greatly reduced the fluorescent intensity of the material.In addition,the twisted tert-butyl group in complex W1 destroyed the plane configuration of the ligand to a certain extent,which led to the weakening of the fluorescence emission of the complex.In contrast,complex W2 had relatively more stable luminous intensity and better light stability under the same external conditions.The thermogravimetric analysis showed that the thermal stability of bromine-substituted complex W3 was lower than that of the other two complexes.Because the thermal stability was related to the bond length of the complex,combined with the above analysis,the average bond length between the central Ir atom of the complex W3 and the auxiliary ligand was the longest and the coordination bond strength was the weakest,so the thermal stability of the complex W3 was the lowest.In general,the detection results showed that all three complexes had good photostability and thermalstability.The emission wavelength and color of triazole ionic iridium complexes could be controlled by introducing electron-donating groups and electron-withdrawing groups into auxiliary ligands.The relationship between structure,photophysical properties and thermal stability was given,and the influence of ligand on photophysical properties of iridium complexes was discussed.