Emissive Osmium(II) Complexes with Tetradentate Bis(pyridylpyrazolate) Chelates

A tetradentate bis­(pyridylpyrazolate) chelate, L, is assembled by connecting two bidentate 3-(trifluoromethyl)-5-(2-pyridyl)­pyrazole chelates at the 6 position of the pyridyl fragment with a phenylamido appendage. This chelate was then utilized in the synthesis of three osmium­(II) complexes, namely, [Os­(L)­(CO)2] (4), [Os­(L)­(PPh2Me)2] (5), and [Os­(L)­(PPhMe2)2] (6). Single-crystal X-ray structural analyses were executed on 4 and 5 to reveal the bonding arrangement of the L chelate. Phosphine-substituted derivatives 5 and 6 are highly emissive in both solution and the solid state, and their photophysical properties were measured and discussed on the basis of computational approaches. For application, fabrication and analysis of organic light-emitting diodes (OLEDs) were also carried out. The OLEDs using 5 and 6 as dopants exhibit saturated red emission with maximum external quantum efficiencies of 9.8% and 9.4%, respectively, which are higher than that of the device using [Ir­(piq)3] as a red-emitting reference sample. Moreover, for documentation, 5 and 6 also achieve a maximum brightness of 19540 cd·m–2 at 800 mA·cm–2 (11.6 V) and 12900 cd·m–2 at 500 mA·cm–2 (10.5 V), respectively.四齿双(吡啶基吡唑根)螯合配体L，通过苯酰胺臂将两个双齿3-(三氟甲基)-5-(2-吡啶基)吡唑螯合单元连接于吡啶片段的6位组装得到。该配体随后被用于合成三种锇(II)配合物，分别为[Os(L)(CO)₂](4)、[Os(L)(PPh₂Me)₂](5)以及[Os(L)(PPhMe₂)₂](6)。研究人员对配合物4和5开展了单晶X射线结构分析，以明确螯合配体L的键合排布模式。膦取代衍生物5和6在溶液与固态下均表现出高强发光性能，研究人员结合计算化学方法对其光物理性质进行了表征与讨论。针对实际应用，研究人员还开展了有机发光二极管（OLED，organic light-emitting diode）的制备与性能表征工作。以5和6作为掺杂剂的OLED器件展现出饱和红光发射，其最大外量子效率分别为9.8%和9.4%，优于以[Ir(piq)₃]作为红光参考样品的器件性能。此外，两款配合物5和6的最大亮度分别为：在800 mA·cm⁻²（11.6 V）下达到19540 cd·m⁻²，在500 mA·cm⁻²（10.5 V）下达到12900 cd·m⁻²。