Kim So-Yoen, Kim Jin-Hyoung, Lee Sanghun, Yun Bo-Sun, Son Ho-Jin, Kang Sang Ook
Department of Advanced Materials Chemistry, Korea University, Sejong30019, Korea.
Inorg Chem. 2022 Nov 21;61(46):18554-18567. doi: 10.1021/acs.inorgchem.2c02890. Epub 2022 Nov 8.
To elucidate the key parameters governing the emission properties of phenylimidazole (pim)-based Ir(III) emitters, including their electronic structure and the bulky aryl substitution effect, a series of pim-based iridium(III) complexes (, = 1-R-2-(X-phenyl)-1-imidazole) bearing secondary pendants of increasing bulkiness [R = methyl (Me), phenyl (Ph), terphenyl (TPh), or 4-isopropyl terphenyl (ITPh)] and three different primary pim ligands (X = F, F, and CN) were designed and synthesized. Based on photophysical and electrochemical analyses, it was found that the excited state properties are highly dependent on the bulkiness of the secondary substituent and the inductive nature of the primary pim ligand. The incorporation of bulky TPh/ITPh substituents in the second coordination sphere significantly enhanced the emission efficiencies in the solid state (Φ = 72.1-84.9%) compared to those of the methyl- or phenyl-substituted Ir(III) complexes (Φ = 30.4% for and 63.7% for ). Further modification of the secondary aryl substituent ( → ) through the incorporation of an isopropyl group and F substitution on the primary pim ligand ( → ) resulted in a slight decrease in the LUMO and a significant decrease in the HOMO energy levels, respectively; these energy level adjustments consequently amplified emission blue shifts, thereby enabling efficient blue electroluminescence in phosphorescent organic light-emitting diodes. Theoretical calculations revealed that the excited-state properties of pim-based Ir(III) complexes can be modulated by the nature of the peripheral substituent and the presence of an EWG substituent. Among the fabricated blue-emitting TPh/ITPh-substituted Ir(III) complexes, , , and were tested as blue-emitting dopants for blue phosphorescent OLEDs owing to their high solid radiative quantum yields (Φ = 75.9-84.9%). The -doped multilayer device displayed the best performance with a maximum external quantum efficiency of 21.0%, a maximum current efficiency of 43.6 cd/A, and CIE coordinates of 0.18 and 0.31.
为阐明控制基于苯基咪唑（pim）的Ir（III）发光体发射特性的关键参数，包括其电子结构和庞大芳基取代效应，设计并合成了一系列带有体积逐渐增大的二级侧基[R = 甲基（Me）、苯基（Ph）、三联苯（TPh）或4-异丙基三联苯（ITPh）]以及三种不同一级pim配体（X = F、F和CN）的基于pim的铱（III）配合物（， = 1-R-2-(X-苯基)-1-咪唑）。基于光物理和电化学分析发现，激发态性质高度依赖于二级取代基的体积和一级pim配体的诱导性质。与甲基或苯基取代的Ir（III）配合物（对于为30.4%，对于为63.7%）相比，在第二配位层中引入庞大的TPh/ITPh取代基显著提高了固态发射效率（Φ = 72.1 - 84.9%）。通过在一级pim配体上引入异丙基和F取代对二级芳基取代基进行进一步修饰（ → ），分别导致最低未占分子轨道（LUMO）略有降低和最高已占分子轨道（HOMO）能级显著降低；这些能级调整相应地放大了发射蓝移，从而在磷光有机发光二极管中实现了高效的蓝色电致发光。理论计算表明，基于pim的Ir（III）配合物的激发态性质可通过外围取代基的性质和吸电子基团（EWG）取代基的存在进行调节。在制备的发射蓝光的TPh/ITPh取代的Ir（III）配合物中，由于其高的固态辐射量子产率（Φ = 75.9 - 84.9%），、和被测试用作蓝色磷光OLED的蓝色发光掺杂剂。掺杂的多层器件表现出最佳性能，最大外量子效率为21.0%，最大电流效率为43.6 cd/A，国际照明委员会（CIE）坐标为0.18和0.31。
