Synthesis And Luminescence Properties Of Platinum(?) And Platinum(?) Metal-organic Phosphorescent Compounds And Their Application In Oleds

In recent years,highly efficient organic light-emitting devices(OLEDs)have become a research highlight in the field of material science and display technology.Among of the vary materials,transition metal complexes especially the cyclometallating complexes paly an important role in the research of phosphorescent materials for the application in OLEDs.In the past two decades,the transition metal complexes bearing N-heterocyclic carbene ligand have developed fast and they attracted continuous attention for their grate application in pharmaceuticals and chemical catalysts.Moreover,these complexes also attracted much attention because of their good photophysical properties such as tunable triplet emission in OLEDs.In this dissertation,we firstly review the materials of platinum(II)complexes bearing NHC ligand,and secondly prepare a highly efficient triplet emitter through novel ligand designs and regulation.In the end,all of the synthesized complexes were fully characterized and the complex with the good photophysical properties was selected to fabricate OLEDs through solution process.The main research contents are summarized as follows:1.The use of organometallic triplet emitters in OLED applications may be complicated when the luminescent complex bears a formal charge.By designing ligands containing pendant closo-monocarborane clusters[CB₁₁H₁₂]^-,it is possible to neutralize the otherwise cationic cores of cyclometalated Pt(II)complexes bearing bis-carbenes,resulting in significantly enhanced photophysical properties.Herein,we report four Pt(II)complexes decorated with a monoanionic closo-monocarborane by coupling the cluster to the classic cyclometallating moiety,phenylpyridine(ppy).All four complexes were fully characterized by NMR,HR-MS,UV-Vis,and cyclic voltammetry.Complexes Pt(bis-NHC)(L₂),Pt(bis-NHC)(L₃)and Pt(bis-NHC)(L₄)(bis-NHC=1,3-propylene-bis(1,3-dihydro-3-butyl-2H-imidazol-2-ylidene);L₂H=3,6-di-tert-butyl-9-(4-(5-(closo-1-CB₁₁H₁₁)pyridin-2-yl)phenyl)-9H-carbazole;L₃H=4-(5-(closo-1-CB₁₁H₁₁)pyridin-2-yl)-N,N-diphenylaniline;L₄H=2-(4-(closo-1-CB₁₁H₁₁)phenyl)pyridine)were characterized by single-crystal X-ray diffraction.Moreover,all four complexes show interesting photophysical behaviors,with complex Pt(bis-NHC)(L₁)(L₁H=5-(closo-12-CB₁₁H₁₁)-2-phenylpyridine)exhibiting a photo-luminescent quantum yield of 97%in a 2 wt%PMMA film.This high efficiency prompted the incorporation of Pt(bis-NHC)(L₁)into an OLED device using solution processing,resulting in green emission with CIE coordinates of(0.28,0.55).The measured maximum external quantum efficiency(EQE_max)was 18.51%,an EQEmax that is among the highest for solution-processed OLED devices containing Pt(II)complexes with simple cyclometalated ppy ligands.2.Four novel cyclometallating platinum(IV)complexes were prepared and fully charaterized.Each of the complexes featureing a pendant closo-monocarborane cluster[CB₁₁H₁₂]^-ligands and two chlorine atoms.The crystal structure of Pt(bis-NHC)(L₄)-Cl₂exhibits an octahedra coordination geometry with two chlorine atoms taking a cis form.The UV-Vis absorption and emission spectra were also measured in nitrogen degassed acetonitrile solution at room temperature.All of the four complexes exhibit broad emission band in the range of 400–500 nm,which tentatively attributed to platinum disturbed intraligand(IL)transitions.What worth to not is complex Pt(bis-NHC)(L₁)-Cl₂ exhibiting a photoluminescent quantum yield of 30.5%in nitrogen degassed acetonitrile solution at room temperature.