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.