2-(2-羟基苯基)吡啶类铱配合物的合成、晶体结构及光物理性能研究

Synthesis,Characterization and Photophysical Properties for Iridium Phosphorescent Complexes with 2-(2-hydroxyphenyl)Pyridine as Auxiliary Ligand

以2-(2-羟基苯基)吡啶为辅助配体,通过改变主配体的结构,合成出3种新的中性铱磷光配合物[Ir(ppy)_(2)(popy),Ir(dfppy)_(2)(popy)和Ir(dmpq)_(2)(popy)],通过元素分析、核磁共振谱和单晶X射线衍射表征了其组成和化学结构。在3种配合物中,中心铱分别和两个主配体的C和N、一个辅助配体的N和O配位形成稍微扭曲的八面体配合物。采用热分析研究了配合物的热稳定性,发现该类配合物的热分解温度均大于300℃,具有较好的热稳定性。并进一步通过紫外可见光谱(UV-Vis)和光致发光光谱探究了配合物的光物理性能,Ir(ppy)_(2)(popy),Ir(dfppy)_(2)(popy)和Ir(dmpq)_(2)(popy)的最大发射波长为529,502和628 nm,在主配体上引入F,发射波长蓝移,随着主配体共轭程度增大,并引入甲基,发射波长红移。

Since the first organic light emitting diodes(OLEDs)was developed in 1987,OLEDs had attracted remarkable amounts of attention and undergone much development,because of several advantages such as their light weight,thin,flexible,stretchable structures,and variable form factors,owing to these advantages,OLEDs had been successfully used in flat-panel displays and solid-state lightings.However,certain problems remained to be solved.For instance,the efficiency,lifetime and the requirement of high-level vacuum,etc.The organic luminescent materials whose performance directly determined the performance of OLEDs,were one of the most crucial materials in OLEDs materials.The development of organic materials began with fluorescent materials,proceeded to phosphorescent materials and thermally activated delayed fluorescent(TADF)materials.To the present,phosphorescent materials were one of the most excellent organic luminescent materials.The phosphorescent materials were mainly transition metal complexes,such as iridium,platinum cuprous complexes,etc.In the investigated transition metal complexes,iridium complexes were the most excellent and promising phosphorescent materials owing to their stable chemical structure,high luminescent efficiency,and tunable emission wavelength over the whole visible region.Up to now,small-molecular iridium complexes with red and green emission had been successfully applied to OLED industry.However,more pervasive application was still compromised by the inadequacy in the luminescent efficiency and purity.To improve the efficiency and lifetime of OLEDs,with the rapid development of OLED industry and people’s pursuit of high-quality image display,searching for new iridium phosphorescent complexes possessing higher efficiency and purer emission color was continuing.The luminescence color of iridium complexes could be regulated by changing the chemical structure of the main or auxiliary ligand.The main ligand played a decisive role in regulation of luminescence color and efficiency,auxiliary ligands could also adjust the luminescence color and efficiency of the iridium complexes.In the past twenty years,a large number of studies had focused on the effect of main ligands on the luminescence properties.The common auxiliary ligands were O^O,N^N and N^O,etc.O^O was the most commonly used auxiliary ligand and had been widely studied.N^O was also a type of important auxiliary and had been rare studied.fac-Ir(ppy)_3 was the typical phosphorescent iridium complexes with green emission,its synthesis was quite difficult.In fac-Ir(ppy)_3,2-phenylpyridine was selected as main ligand.Using the 2-(2-hydroxyphenyl)pyridine,the synthesis method was simpler than fac-Ir(ppy)_3,and 2-(2-hydroxyphenyl)pyridine was using as auxiliary ligand owing to its structure similar to 2-phenylpyridine,which may have unexpected results.Therefore,three new neutral iridium phosphorescent complexes,[Ir(ppy)_(2)(popy),Ir(dfppy)_(2)(popy)and Ir(dmpq)_(2)(popy)]were designed and synthesized by using 2-(2-hydroxyphenyl)pyridine as auxiliary ligand,and 2-phenylpyridine,2,4-difluorophenylpyridine,and 3,5-dimethylphenylquinoline as the main ligands.Their composition and chemical structure were characterized by elemental analysis,nuclear magnetic resonance spectroscopy and single crystal X-ray diffraction.The structure representation result showed that all the three complexes,central iridium atom coordinates with C and N of two main ligands to form two stable five-membered chelated rings,with N and O of one auxiliary ligand to form a stable six-membered chelating ring,the whole molecule presented a hexacoordinated octahedral geometry.The angle parameters indicated that these complexes had a slightly distorted octahedral cofiguration.Ir(ppy)_(2)(popy)was a yellow columnar crystal with P-4 space group and Tetragonal crystal system,Ir(dfppy)_(2)(popy)was a yellow columnar crystal with I12/a1 space group and monoclinic crystal system,and Ir(dmpq)_(2)(popy)was a red columnar crystal with P121/c1 space group and monoclinic crystal system.Ir-O bond length of Iridium with O in 2-(2-hydroxyphenyl)pridine was longer than Ir-C bond length of iridium with the main ligand,this result indicated that the five-membered ring was more stable than the six-membered ring.The thermal stability of the complexes was studied by thermal analysis.It was found that the thermal decomposition temperature of these complexes was greater than 300℃,which could meet the needs for preparing OLED by vacuum evaporation.The photophysical properties of the complexes were further investigated by ultraviolet and visible spectrophotometry(UV-vis)and photoluminescence spectra.The maximum emission wavelengths of Ir(ppy)_(2)(popy),Ir(dfppy)_(2)(popy)and Ir(dmpq)_(2)(popy)were 529,502 and 628 nm,respectively.The luminous color changes from blue-green,green to deep red.The main ligands with different structures exerted the greatest influence on the emission wavelength and color of iridium complexes.For 2-(2-hydroxyphenyl)pyridine iridium complexes with different main ligands,their maximum emission wavelength varied between 502 and 628 nm,a difference of as high as 126 nm.The increase of conjugation degree of the main ligands and the introduction of methyl group led to the red shift of the emission wavelength,and the introduction of F on cyclometalated ligands led to the blue shift of emission wavelength.Using Ir(ppy)_(2)(popy)as a reference,the maximum emission wavelength of Ir(dfppy)_(2)(popy)was shifted from 529 to 502 nm,and the blue shift was 27 nm,the maximum emission wavelength of Ir(dmpq)_(2)(popy)was red shifted from529 to 628 nm,and the red shift was 99 nm.