Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (05): 1115-1122.doi: 10.3866/PKU.WHXB201302253

• PHYSICAL CHEMISTRY OF MATERIALS • Previous Articles    

Synthesis and Optoelectronic Properties of a Red-Emitting Iridium(III) Complex Containing 1-Phenylpyrazole

REN Jing-Kun1, XU Hui-Xia2,3, QU Li-Tao1, Zhang Ye1, HAO Yu-Ying1,2, WANG Hua2,3, XU Bing-She2,3   

  1. 1 Department of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, 030024, P.R. China;
    2 Research center of Advanced Material science and Technology Taiyuan University of Technology, Taiyuan, 030024, P.R. China;
    3 Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Taiyuan, 030024, P.R. China
  • Received:2012-12-05 Revised:2013-02-25 Published:2013-04-24
  • Supported by:

    The project was supported by the Program for Changjiang Scholar and Innovation Research Team in University, China (IRT0972), International Science & Technology Cooperation Program of China (2012DFR50460), National Natural Science Foundation of China (21071108, 60976018, 21101111, 61274056, 61205179), Natural Science Foundation of Shanxi Province, China (2010021023-2, 2011021022-2), and Key Scientific and Technological Project of Shanxi Province, China (20120321019).

Abstract:

The synthesis, characterization, photophysical and electrophosphorescent properties of iridium(III) complex [(ppz)2Ir(piq)] (ppz=1-phenylpyrazole, piq=1-phenylisoquinoline) are reported. The structure was defined by proton nuclear magnetic resonance (1H NMR). The photophysical properties and energy-level structure of [(ppz)2Ir(piq)] are studied by ultraviolet-visble (UV-Vis) absorption, fluorescence, and phosphorescent spectroscopies at 77 K, cyclic voltammetry (CV), and time-dependent density functional theory (TD-DFT) calculation. The electroluminescent properties of [(ppz)2Ir(piq)] using 4,4'-bis(9-carbazolyl)-1, 1'-biphenyl (CBP) as a host are investigated. Absorption bands of [(ppz)2Ir(piq)] are located at about 296, 342, 395, and 442 nm. [(ppz)2Ir(piq)] exhibits red phosphorescent emission with a peak at 618 nm in CH2Cl2 solution at room temperature and 598 nm in 2-methyltetrahydrofuran (2-MeTHF) at 77 K, from which its triplet state energy (ET) is estimated to be 2.07 eV. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of [(ppz)2Ir(piq)] are -5.92 and -3.62 eV, respectively. A theoretical calculation reveals that the HOMO of [(ppz)2Ir(piq)] is mainly distributed on ppz and the iridium ion, while the LUMO is mainly centered on piq. Organic light-emitting diodes (OLEDs) containing [(ppz)2 Ir(piq)]- doped CBP emitting layer exhibit an electroluminescence (EL) maximum at 616 nm, an optimized doping concentration of 8%-12% (w), maximum current efficiency of about 10 cd·A-1, maximum power efficiency of 4.44 lm·W-1, and International Commission on Illumination (CIE) coordinates of (0.65, 0.35). This investigation provides an important experimental basis for the application of [(ppz)2Ir(piq)] in organic electroluminescent devices.

Key words: Red phosphorescence material, 1-phenylphrazole, 1-phenylisoquinoline, Optoelectronic characteristic, Doping concentration