Near‐Infrared OLEDs Based on Functional Pyrazinyl Azolate Os(II) Phosphors and Deuteration

Abstract Near‐infrared (NIR) emitting Os(II) complexes [Os(L1)₂(PPhMe₂)₂] (tz1), [Os(L2)₂(PPhMe₂)₂] (tz2), and [Os(L3)₂(PPhMe₂)₂] (tz3), bearing dual (1H‐1,2,4‐triazol‐5‐yl)pyrazine chromophoric chelates, are successfully developed. These pyrazine chelates tzn (n = 1, 2, 3) differ by the location and number of 4‐(trifluoromethyl)phenyl appendage(s) on pyrazine, and the associated Os(II) complexes exhibit bathochromic shifted emission, higher quantum yield, and increased radiative lifetime in comparison to parent complex [Os(fprtz)₂(PMe₂Ph)₂] (tz0). Moreover, partially deuterated pyrazine chelate L1‐d is prepared using post‐synthetic deuteration, from which the Os(II) complex tz1 shows a photoluminescence quantum yield (PLQY) of 12.2% in co‐doped 4,4′‐bis(N‐carbazolyl)biphenyl (CBP) thin film at 3 wt%. Further, the partially deuterated tz1‐d exhibits a notable increase in PLQY to 17.8% upon co‐deposited into CBP thin film, confirming the influence of C‐H(D) stretching vibrations on the non‐radiative transition processes. Finally, tz1‐d is demonstrated to be suitable in the fabrication of efficient NIR organic light‐emitting diodes (OLEDs), from which max. external quantum efficiency of 3.77% and max. radiance of 24.1 W sr^‐1 m^‐2 are recorded for emission with peak maximum at 776 nm. These experiments confirm the suppression of C–H vibration caused quenching by deuteration, which should be broadly applicable to the OLED emitters, especially in the NIR region.