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

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.

Automated summary

Near-infrared emitting Os(II) complexes with improved emission properties and increased radiative lifetime are successfully developed by introducing 4-(trifluoromethyl)phenyl on pyrazine. The influence of C-H(D) stretching vibrations on non-radiative transition processes is confirmed, leading to the fabrication of efficient NIR organic light-emitting diodes.