Synthesis And Electroluminescence Of Iridium(Ⅲ) And Zinc(Ⅱ)Complexes Based On Benzothiazole Ligands

In this dissertation, by modifying the ligand framework, we designed and synthesized a series of cyclometalated iridium(Ⅲ) and zinc(Ⅱ) complexes bearing benzothiazole as the basic moiety. We also explored the relationships between the luminescent property of complex and the structure of cyclometalated ligand or the type of substitutes. The specific works are as follows:(1) A series of iridium complexes were designed and synthesized by introducing different electron-withdrawing and-donating substituents into the benzothiazole ring of the2-phenylbenzothiazole ligand, and their electroluminescent performances were also investigated. There are three parts in this work:Heteroleptic bis-cyclometalated iridium complexes:By introducing different electron-withdrawing and electron-donating substituents (-CF3,-F,-CH3,-OCH3) into the benzothiazole ring, four2-phenylbenzothiazole derivatives were prepared as the cyclometalating ligands. Their orange-emitting heteroleptic iridium complexes were designed and then synthesized:Ir(tfmbt)2(acac), Ir(fbt)2(acac), Ir(mbt)2(acac) and Ir(mobt)2(acac). The substituent effect on the electroluminescent performance of these complexes was studied. Complexes Ir(tfmbt)2(acac) and Ir(fbt)2(acac) based orange organic light-emitting diodes (OLEDs) exhibit excellent device performances with maximum luminance efficiencies of76.0cd A-1and71.6cd A-1, respectively. Two-element white OLEDs were fabricated by using these two complexes in combination with the blue-emitting Firpic. and highly efficient white light emission with the peak efficiencies of68.6cd A-1and26.2%was realized, which are some of the highest efficiencies ever reported for two-element WOLEDs so far.Homoleptic tris-cyclometalated iridium complexes:Using the aforementioned heteroleptic complexes as starting materials, four homoleptic tris-cyclometalated iridium (Ⅲ) complexes containing2-phenylbenzothiazole derivatives as ligands. Ir(fbt)3, Ir(mbt)3, Ir(mobt)3and Ir(bt)3. have been successfully synthesized for the first time by adopting a new synthetic route. OLEDs were fabricated by using these complexes as doped emitters. Among them, the pristine complex Ir(bt)3based OLED exhibited excellent performance with a turn-on voltage of4.2V, a maximum luminance of95800cd m-2, maximum efficiencies of29.6%.87.9cd A-1and46.0lm W-1at6V, which are all almost the best data ever reported for orange OLEDs so far. Especially, the luminance efficiency of87.9cd A-1is almost double of the highest data ever reported for orange OLEDs in literatures.Solution-processible cyclometalated iridium complexes:By introducing hole-transporting N-phenyl-1-naphthylamino moieties into the benzothiazole ring of2-phenylbenzothiozole ligand, two cyclometalated iridium complexes, Ir(NPA-bt)3and Ir(NPA-bt)2(acac), have been synthesized. The presence of electron-donating and bulky N-phenyl-1-naphthylamino groups is beneficial to a red-shifted emission, raised the HOMO levels, improved the solubility and good film-formation quality of the resulting complexes. Solution-processed OLEDs containing these complexes as the guest dopants exhibit orange-red electroluminescence and good device performances. In addition, two-element white OLEDs were achieved with these orange-red phosphors and the blue Firpic by spin coating the emission layer. White emissions with high color purity were achieved by simply adjusting the blending ratio between the two emitters.(2) By fixing benzothiazole as the N-related heteroaromatic moiety and selecting different aryl as C-related aromatic ring, we synthesized four novel2-arylbenzothiazoles as cyclometalated ligands frameworks. Seven homoleptic and heteroleptic cyclometalated iridium complexes were then synthesized by using these new ligands. By adjusting the intramolecular charge transfer extent within ligand, varying the π-conjugation length in the cyclometalated ligand, and introducing auxiliary ligand with higher electric field, the phosphorescence peak wavelength of the resulting seven iridium complexes are continuously tuned from yellow to saturated red. We further investigated the substitute effect on the photophysical and electrochemical behaviors of these phosphors and their application on the OLEDs. Complex Ir(3-Cz-bt)3based OLED showed the best device performance with a maximum luminance of51220cd m-2. a maximum efficiency of75.90cd A-1.48.19lm W-1and23.00%.(3) By introducing different electron-withdrawing or electron-donating groups on the different positions of2-(2-hydroxyphenyl)benzothiozole (BTZ) ligand. eight novel Zn(BTZ)2derivatives were designed and synthesized. We investigated their luminescent properties, energy levels and electroluminescent behaviors. It is well demonstrated that the introduction of electron withdrawing group on benzothiozole frame can effectively lower the LUMO levels of these complexes and improving their electron-injecting ability. Different substitutions on the cyclometalated ligands rendered large influences on the spectral features of these complexes. Among them, the OLED based on complex4exhibited a CIE coordinates of (0.37,0.36) at10V. being quite close to the pure white light (0.33,0.33), which promises complex4a potential component for white electroluminescence.