Orange–Yellow Phosphorescent Iridium(III) Complex for Solution-processed Organic Light-Emitting Diodes: Structural, Optical and Electroluminescent Properties of Bis(2-phenylbenzothiazole)[2-(2-hydroxyphenyl)benzothiazole]iridium(III)

New orange–yellow phosphorescent cyclometalated iridium(III) complex, (bt)2Ir(btz), where btH = 2-phenylbenzothiazole and btzH = 2-(2-hydroxyphenyl)benzothiazole, was synthesized, and its structural, photophysical and electroluminescence properties were investigated to apply for organic light-emitting diodes (OLEDs) applications. The coordination geometry around iridium metal ion was distorted octahedral, exhibiting cis-C, C′ and trans-N, N′ chelate dispositions with narrow ligand bite angles ranging from 79.7° (2) to 84.5° (1). The optical properties revealed that the π-conjugated nature of bt ligand caused a bathochromic shift in emission and btz ligand played a role in fine color tuning. The synthesized (bt)2Ir(btz) was soluble in common organic solvents and the emitting layer was readily spin-coated in chlorobenzene solution onto substrate. The OLED fabricated with the configuration of ITO/PEDOT:PSS/PVK:TCTA:OXD-7: (bt)2Ir(btz) (32:32:28:8)/Bphen/LiF/Al exhibited a maximum external quantum efficiency (EQE) of 4.67% and a maximum luminance efficient (LE) of 8.61 cd/A with CIE (x, y) coordinates of (0.54,0.45).