Syntheses, Structures And Properties Of Novel Phosphorescent Iirdium Complexes

Organic Light-Emitting technology has received much more attentions because of itsbrilliant colors, outstanding display effect. After twenty years rapid development, a largenumber of materials suitable for electroluminescent have been developed, especially theapplication of phosphorescent complexes. Due to the very high efficiency and brightness,phosphorescent complexes must have great potential applications. Generally, to realizehigh performance phosphorescent OLEDs (PHOLEDs), the phosphorescent materials mustbe doped as emitting guests into some appropriate fluorescent host matrixes in a rather lowand narrow concentration range, due to their undesired luminescence self-quenching andpoor carrier mobility. Because the device efficiency is sensitive to the dopingconcentration, reproducing the device fabrication process becomes very hard and precisefabrication technologies must be employed. Considering the problems mentioned above,we designed and synthesized a series of novel iridium complexes containing of amidinateor guanidinate ancillary ligand, investigated their crystal structure, photophysicalproperties, electrochemical properties, thermal stability and electroluminescent properties,and discussed the relationship between material structure and properties.1. In chapter II, by using different cyclometalating ligands and modificating theancillary ligands, we designed and synthesized a series of novel iridium complexes. Theirstructures were characterized by NMR, elemental analyses, and mass spectra. These noveliridium complexes with N^N coordinated ancillary ligands are different from thetraditional C^N or O^O coordinated ancillary ligands, and the metallacycle formed byC···N···Ir···N four atoms is more rigid than the five or six-membered metallacycle formed by the C^N ligand or O^O ligand. On the other hand, introduction of the electron-richeddouble N ligand can make the electron-deficient central atom Ir (III) more stable. For themodification of ancillary ligands, we used some electron-withdrawing or electron-donatinggroups, and introduced some groups with large conjugate plane, together with the changeof the first ligands, we achieve the purpose of tuning the emitting of the iridiumcomplexes.2. In chapter III, eight crystals were obtained by the vaccum sublimation, and thestructures were calculated from X-ray diffraction data. We have systematicallyinvestigated their crystal structures. There are no strong intermolecular π···π interactions inthe crystal packing of these compounds, which should attribute to the large steric hindranceof the octahedral structure of the iridium complexes. There are only compound1,3,4haveweaker π-π intermolecular interactions in the crystal structure, compound1exists C-H···πintermolecular interaction, and existence of C-H···F intermolecular interactions incompound10, other compounds have no special intermolecular interaction in the crystalstructures except van der Waals force. The lack of strong intermolecular interactions isfavorable for preventing the undesired self-quenching of the phosphorescence.3. In chapter IV, We have systematically investigated the thermal, electrochemicaland photophysical properties of the complexes we have synthesised. In addition, we carriedout theoretical calculations for some of these compounds to investigate their electronicstructures, and discussed the carrier transport characteristics. At the meantime, weinvestigate the structure-property relationship of these materials. Thermodynamic Propertytests show that using rigid the first ligand, enlarging the conjugated π system of the firstligand and introducing rigid groups to the ancillary ligands, are beneficial to improve thethermal stability of the compounds. In contrast, introducing F to the first ligands or flexiblegroup to the ancillary ligands may reduce the thermal stability of the compounds. All thecompounds have good thermal stability, suitable for the fabrication of organicelectroluminescent devices. Photophysical properties tests show that, the first ligands ofiridium complexes have a great impact to UV-visible absorption. For example compound1(Fppy)2Ir(dipba) has a blue shift of approximately80nm Compared with the absorption peak of compounds4(bt)2Ir(dipba). At the meantime, the change of auxiliary ligand alsohave a certain impact to UV-visible absorption bands. Such as compound6(ppy)2Ir(tipg)compared with compound11(ppy)2Ir(dipcca), which have the same first ligand, bychanging the substituted group of ancillary ligand caused absorption peak change of about30nm. This result reveals that the auxiliary ligand take part in the MLCT and LCtransitions of the complexes. The emission of iridium complexes we designed andsynthesized cover nearly the entire range from499nm blue-green to680nm deep red. Thefirst ligands play a decisive role in the emission of complexes, and the change ofSubstituent of ancillary ligands can fine tuning the luminescent. All the complexesdisplayed oxidation wave in dichloromethane. No reduction wave was detected within theelectrochemical window of dichloromethane. The highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels werecalculated from the cyclic voltammetry (CV) data together with the absorption spectra. Allthe HOMO energy levels are among-4.78to-5.27eV much higher than common iridiumcomplexes. In the organic light emitting devices, the high HOMO energy levels indicatethat the hole can inject smoothly. Theoretical calculation results indicate that, theintroduction of Guanidinate or amidinate ligands to iridium complexes made lots of theHOMO orbit distributed to the ancillary ligands, which caused the rise of the HOMOenergy level, and little effect on the LUMO energy level. This result is consistent with theelectrochemical test. Carrier mobility tests show that the complexes have very highelectron and hole mobility, which may be related with the dispersion of the HOMO and theLUMO orbits.4. In chapter V, We selected several of the iridium complexes for fabricating organiclight emitting devices. All the monochromatic and white devices exhibit quit low turn-onvoltages and rather high efficiency, even with high dopant concentrations or non-dopedemitting layer. The high efficiency should attribute to the higher HOMO energy level andhigher electron and hole mobility, and the balance of hole and electron in emitteing layerenhance the formation of exciton and recombination greatly. Compound3doped incompound1as emitting layer, we fabricated high performance devices. With the doping concentration of8%, the maximum power efficiency31.6lm W-1was gotten at voltage of3.5V and brightness of172cd m2, and the maximum external quantum efficiency was13.8%at voltage of4V. Compound1has Matched energy levels to eletron and holetransporting layers, good charge mobilities and higher triplet level. This results reveal thatCompound1is not only a good phosphorescent guest material for fabricating highperformance green emitting device, but also a excellent host material for orange to redphosphorescent guest.In summary, we have obtained a series of novel iridium complexes through the designand modification of first ligands and ancillary ligand. The structures and properties of thesecompounds were characterized, and the relationship between structure and property waselucidated. Apply the complexes in PHOLEDs, we get a series of high performancedevices with high doped concentration even non-doped emitting layers.