 This study investigates the effect of targeted deuteration on donor and acceptor units of thermally-activated delayed fluorescence emitters in blue organic light-emitting diodes, revealing that deuteration of the acceptor unit is critical for enhancing photostability in device lifetime. The results show a gradual increase in device operational stability, achieving a long lifetime time of 90% of initial luminance for 23.4H at 1000 candelas M2 luminance. This study highlights the importance of structural modification materials at a subatomic level towards prolonging device operational stability. This article was authored by Xin Yong Chung, Yilong Chung, Psy Jelly, and others.