The Synthesis And Properties Study Of Cyclometalated Iridium Complexes With Oxadiazole-based Picolinic Acid Which The Liquid-crystal Groups Were Induced Into

Cyclometalated Iridium (III) complexes have became the significant research in the electrophosphorescent field because of their better ability such as high luminescent efficiency, shorter phosphorescent life and the convenience to finely tune the color by suitable modification of the structure of the ligands. The 1,3,4-oxadiazole (OXD) derivatives is a class of electron transporting materials which are widely applied and studied in OLEDs due to their excellent electron transporting and light-emitting properties, as well as thermal and chemical stability. Based on the above mentioned idea, six picolinic acid derivatives containing liquid crystal unit and oxadiazole functional group have been firstly designed and synthesized. Then using these picolinic acid derivatives as ancillary ligands and 2, 4-diflurophenyl pyridine as cyclomatalated ligand, a series of blue-emitting cyclometalated iridium (III) complexes were synthesized, their chemical structures have been characterized by the 1H NMR and elemental analysis.These cyclometalated iridium (III) complexes exhibited good solubility and can dissolve in common solvents. Their UV absorption and photoluminescence properties were studied. The results displayed that these cyclometalated iridium complexes had an intense absorption band at the range from 250 nm to 450 nm and a strong emission peak at around 470 nm, which indicats that these cyclometalated iridium complexes have a better photoluminescenct performance at photo-excitation.The electrochemical properties of these cyclometalated iridium complexes were also studied by cyclic voltammetery. According to the oxidation-reduction potention, ttheir high ocupation molecular orbit (HOMO) and lowest unocupation molecular orbit (LUMO) energy levels were calculated.The thermal stability of these iridium complexes were then studied through differential thermal analysis(DSC) and thermal thermogravimetric analysis(TGA). The thermodynamics and liquid crystals properties of the ancillary ligands were investigated by polarizing microscope. The results indicated that the glass transition temperature and melting point of the ancillary ligands decreasedwith the growth of flexible side chain length.Using a blend of poly(vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl -1,3,4-oxadiazoles (PBD) as host matrix and these cyclometalated iridium complexes as guest materials, the single-layered polymer light-emitting devices were fabricated and their electroluminescent prperties were studied. The self-innovational cyclometalated iridium complexes containing oxadizole functional group and its polymer light-emitting devices were achieved. A highest external quantum efficiency of 0.27% was achieved in the devices at 4wt.% dopant concentration. However, we have not displayed satisfactory luminous efficiency. It is necessary for high-efficiency PLEDs to further optimize device configuration.