Synthesis And Optical Properties Of 2-phenylpyridine Pt(â…¡) Complexes

In recent years,organic light emitting diodes(OLEDs)have replaced traditional liquid crystal displays(LCDs)as a great research topic for many researchers.As a member of OLED luminescent materials,Pt(Ⅱ)complexes can theoretically achieve 100%internal quantum efficiency(IQE)with high phosphorescence performance due to their simultaneous use of singlet and triplet exciton emission.It can effectively solve the problem of low efficiency of fluorescent materials.By structural modification of the ppy-ligand in the ppyPt(β-diketonate)complex,the functional groups of the main group elements with different characteristics can be introduced,which can effectively control the luminescence of the complex and improve the electron transport properties of the resultant complexes.So far,a large number of Pt(Ⅱ)complexes functionalized by main group elements have been reported in detail.The main group elements such as boron,nitrogen,oxygen and sulfur have been widely used in the syntheses of Pt(Ⅱ)complexes.However,there are few reports on the molecules containing heavy elements of the main group.It is also unknown whether the heavy elements of the main group could affect the photoelectric properties of the Pt(Ⅱ)complex.For the first time,the same main group element was introduced into the organic ligand,and a series of ppyPt(β-diketonate)complex of benzo[b]furan,benzo[b]thiophene,benzo[b]selenophene and benzo[b]porphin were synthesized,in which two complexes contain heavy elements such as selenium and tellurium.Their structures were confirmed by nuclear magnetic resonance spectroscopy(NMR)data and X-ray single crystal diffraction.From the single crystal data of Pt-Se and Pt-Te,it is found that there is a certain difference by comparison with ordinary C-Se bond and C-Te bond,and it is speculated that benzo[b]selenophene and benzo[b]porphin have a certain aromaticity.Cyclic voltammetry(CV)showed that they have better electron transport properties,and TG and DSC also displyed that they possess better thermal stability.The experimentally measured spectral data is in good agreement with the calculated simulated spectral data,in which Pt-S exhibits slightly different spectral characteristics from the other three complexes.It is speculated that this may be related to the aromaticity of the benzo[b]thiophene.Most importantly,for the first time,the reported results should reveal an overall prospect for the effect of the atoms in group VIA on the properties of the ppyPt(β-diketonate)complexes.Similar to conventional organic fluorescent materials,some cyclic Pt(Ⅱ)complexes often exhibit lower luminescence intensity at high concentrations or in solid state,which greatly limits their application in OLEDs.The luminescent materials having the characteristics of aggregation induced emission(AIE)have high quantum yields at high concentration or solid state,and can effectively solve the aggregation-caused quenching(ACQ)phenomenon of the conventional fluorescent materials.The development of new Pt(Ⅱ)complexes with AIE properties is undoubtedly an effective way to improve OLED efficiency.In this paper,a series of Pt(ppy)(N-donor ligand)Cl complexes with AIE properties were designed and synthesized,with triphenylamine as the ring metal ligand,and the N-donor ligand increase the complex’s hole injection/transporting(HI/HT)and electron injection/transporting(EI/ET)by introducing functional groups of the main group elements of different electronic properties.All the complexes were identified by NMR,and their AIE properties were determined in detail.The experimental results show that when the N-donor ligand is triphenylphosphine oxide,the Pt-OP series exhibits a higher AIE performance.Therefore,three Pt-ppyOP complexes were synthesized with ppyas the ring metal ligand and triphenylphosphine oxide as the N-donor ligand.TG indicated that the temperature at which most of the complexes lost 5%weight was above 300 ~oC,which showed good thermal stability.In addition,we also synthesized a series of complexes with multiple metal coordination centers.The experimental results show that the UV absorption spectrum and the photoluminescence spectrum have almost no change with the increase of the metal coordination center,but the AIE spectrum shows a certain difference,which may be related to the steric hindrance of the complexes.To date,there is almost no multinuclear complex with AIE properties have been reported,which has undoubtedly provided a new idea for the development of high-efficiency electroluminescent devices.