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

The synthesis, characterization, photophysical and electrophosphorescent properties of iridium(III) complex [(ppz)(2)Ir(piq)] (ppz=1-phenylpyrazole, piq=1-phenylisoquinoline) are reported. The structure was defined by proton nuclear magnetic resonance (H-1 NMR). The photophysical properties and energy-level structure of [(ppz)(2)Ir(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)(2)Ir(piq)] using 4,4'-bis(9-carbazolyl)-1, 1'-biphenyl (CBP) as a host are investigated. Absorption bands of [(ppz)(2)Ir(piq)] are located at about 296, 342, 395, and 442 nm. [(ppz)(2)Ir(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 (E-T) is estimated to be 2.07 eV. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of [(ppz)(2)Ir(piq)] are -5.92 and -3.62 eV, respectively. A theoretical calculation reveals that the HOMO of [(ppz)(2)Ir(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)(2)Ir(piq)] in organic electroluminescent devices.