Synthesis, Characterization And Luminescent Properties Of Multifunctional Organic Molecules And Iridium(â…¢) Complexes

Organic light-emitting devices (OLEDs) have attracted intensive attention due to their unique advantages in the field of modern display technique. It is well known that OLED materials must possess high luminescent efficiency and excellent carrier transport ability. That results in the limited use of luminescent materials in this field because of their deficiency. Although it is discovered that the performance of holes transporting materials is better than that of electrons transporting materials, the imbanance between injection and transportation of holes and electrons in the luminescent layer limits the luminescent efficiency. One of effective way to overcome this problem of luminescent materials is to obtain organic luminescent molecules, which possess of both light-emitting center and carrier transport units at the same time. Therefore, in this thesis, we will synthesize this kind of new materials by chemical methods.1. As well known, triphenylamine (TPA) groups which possess superior hole-transport mobility, low ionization and good resolvability, are extensively used as hole transporting materials in EL. Compounds containing 1,3,4-oxadazole (OXA) which possess excellent electron affinity, good light-emitting, thermal stability, and chemical stability characteristic, are commonly used as electron transporting and hole blocking materials in OLEDs. In this contribution, we report the synthesis of four multifunctional organic molecule, N-phenyl-N-(4-(5-(pyridin-4-yl)-1,3,4-oxadiazol -2 -yl)phenyl)benzenamine (I), N-phenyl-N-(4-(5-(2-phenylpyridin-3-yl)-1,3,4- oxadiazol-2-yl)phenyl)benzenamine (II), N-phenyl-N-(4-(5-p-tolyl-1,3,4-oxadiazol-2- yl)phenyl)benzenamine (III) and N-phenyl-N-(4-(5-(2-phenylquinolin-4-yl)-1,3,4- oxadiazol-2-yl)phenyl)benzenamin (IV), which contain hole-transporting TPA, electron-transporting OXA and light-emitting units in the molecule. These compounds have been characterized by 1H-NMR, FI-IR spectra and elemental analysis. In addition, the crystals of (I) and (II) were cultivated and characterized using X-ray crystallography. Their photophysical properties are also investigated by UV-vis and photoluminescence (PL) spectroscopy. It has been found that the PL spectra of (I), (II) and (III) red shift with increased solvent polarity, and they emits bright bluish green or blue light in ethyl acetate. The corresponding maxima emission locate at 468, 451 and 435nm, respectively. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of (I) and (II) are deduced by the calculations of density function theory (DFT) at B3LYP/6-31G. To investigate the electroluminescence properties of (III), we fabricated devices with structure ITO/PEDOT(50nm)/PVK:compound(87:22)(70nm)/Ca(10nm)/Al(100nm) by spin-coating technique. The maxima emission of EL is 437nm. The turn-on voltage, maximum efficiency, and brightness for blue emission obtained from the device are 6V, 0.50cd/A and 717cd/m2, respectively.2. Because of the merits of Iridium(III) complexes, such as high luminescent efficiency, shorter phosphorescent life, the possibility to finely tune the color by suitable modification of the structure of the ligands, we synthesized two Ir(III) complexes, (mpp)2Ir(tta) and (ppy)2Ir(dMbpy)+·PF6-. The crystals of (mpp)2Ir(tta) and (ppy)2Ir(dMbpy)+·PF6- were cultivated and characterized using X-ray crystallography. Their photophysical properties are investigated by UV-vis and PL spectroscopy. The HOMO and LUMO levels of the two complexes are deduced by the calculations of density function theory (DFT).