Deuterated Radical Emitters Achieve 10.8% EQE at 800 nm with Remarkably Enhanced Operational Stability

Near-infrared (NIR) radical emitters are promising for organic light-emitting diodes (OLEDs) but are limited by low emission efficiency and operational stability. Here, we demonstrate that C–H perdeuteration markedly enhances the performance of both the benchmark TTM-TPA radical and a red-shifted analogue, PyBTM-TPA. Photoluminescence quantum yields increase from 24.0% to 30.7% for TTM-TPA and from 7.3% to 10.4% for PyBTM-TPA. Deuterated devices also exhibit improved performance, achieving record maximum external quantum efficiencies (EQEmax) of 10.81% at peak wavelength 800 nm and 3.56% at 865 nm for perD-TTM-TPA and perD-PyBTM-TPA, respectively, together with extended operational lifetimes. We further reveal that the isotope effect is governed by molecular reorganization energy, determined by both the effective Huang–Rhys factor and the distribution of vibronic coupling among individual vibrational modes. These findings establish deuterium engineering as a general strategy for improving radical-based NIR-OLEDs. Near-infrared organic radical emitters are promising, but their efficiency and stability remain limited. Wang et al. used deuterium substitution to enhance emission, device performance, and lifetime, and identified the factors governing isotope-driven improvements.