Heteroleptic Ir(iii) phosphors with bis-tridentate chelating architecture for high efficiency OLEDs

Abstract

Two tridentate chelates derived from functional 1,3-dipyridin-2-yl benzene, i.e. 1,3-difluoro-4,6-di(pyridin-2-yl) benzene (L1-H), 1,3-difluoro-4,6-di(4-t-butylpyridin-2-yl) benzene (L2-H), 1,3-di(pyridin-2-yl)-5-t-butylbenzene (L3-H), and 1,3-di(isoquinolinyl)-5-t-butylbenzene (L4-H), and 2-pyrazol-3-yl-6-phenylpyridine, 2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(4-trifluoromethylphenyl) pyridine (L5-H₂) and 2-(5-trifluoromethyl-1H-pyrazol-3-yl)-6-(4-t-butylphenyl) pyridine (L6-H₂), were synthesized. These chelates are classified as the monoanionic and dianionic chelates according to the number of active hydrogen atoms present. Treatment of L1-H–L4-H with IrCl₃·3H₂O afforded chloro-bridged dimers [Ir(Ln)Cl(μ-Cl)]₂ (n = 1–4); incorporation of secondary chelates L5-H₂ and L6-H₂ led to the formation of six judiciously selected, charge-neutral, bis-tridentate Ir(III) complexes, namely, [Ir(L1)(L5)] (1), [Ir(L2)(L5)] (2), [Ir(L3)(L5)] (3), [Ir(L3)(L6)] (4), [Ir(L4)(L5)] (5), and [Ir(L4)(L6)] (6). Detailed characterization and photophysical measurements have been performed, and computational calculations have been carried out to shed light on the enhanced emission efficiency and color tunability. This work further investigated the green-emitting and red-emitting organic light-emitting diode (OLED) applications of Ir(III) complexes 1 and 5, respectively. As a result, a maximum external quantum efficiency of 13.2%, luminance efficiency of 41.4 cd A⁻¹, and power efficiency of 35.5 lm W⁻¹ were obtained for the green OLED (complex 1), as opposed to 15.4%, 21.0 cd A⁻¹, and 16.3 lm W⁻¹ for the red-emitting OLED device (complex 5). The high electroluminescence efficiencies suggest the great potential of the titled complexes for applications in multicolor OLED displays.