Deuterated Multiple‐Resonance Thermally Activated Delayed Fluorescence Emitter and Their Application in Vacuum‐Deposited Organic Light‐Emitting Diodes

Abstract Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters have garnered significant attention in recent years due to their remarkable properties, such as high luminescent quantum yield, robustness, and their compliance with the Broadcast Television 2020 standard for the new generation of ultrahigh‐definition. Despite these advancements, the operational lifetimes of organic light‐emitting diodes (OLEDs) relying on MR‐TADF emitters still fall short for practical application. It is believed that the enhancement of the intrinsic molecular stability of ^tBu‐DABNA, a fundamental backbone of MR‐TADF emitters, holds great promise to be a universal strategy for all MR‐TADF emitters improving the operational lifetimes of OLEDs. Herein, the design and synthesis of targeted deuteration are reported on donor and/or backbone of MR‐TADF emitters, where the structure‐property relationship between intrinsic molecular stability upon isotopic effect and device operational stability are examined. The isotopic analogs show a gradual increase in the device operational stability and achieve long‐lifetime LT₈₀ (80% of the initial luminance of 1000 cd m⁻²) of 24.3 h for TADF‐sensitized fluorescence OLED, representing a sevenfold enhancement when compared with the undeuterated counterpart. This strategic deuteration approach underlines the importance of structural modification on materials toward device operational stability.