Of particular note, deuteration has recently attracted much attention in the literature as an effective strategy for promoting device stability due to the kinetic isotope effect , although such an effect can be traced back to 2010, when it was first observed in a green phosphorescent emitter . Choi and Baik et al. recently realized a double enhancement on LT70 of blue PhOLEDs through deuterating the most vulnerable benzylic C-H bond in a blue Irphenylimidazole dopant to hamper the deactivation pathway involving C-H/D bond cleavage notably . In this year, our group also explored the perdeuteration strategy for sky-blue TADF materials and obtained a three-fold longer device lifetime . It was found that the isotopic substitution could suppress the high-frequency structural vibrations of TADF emitters, not only extending the operational lifespan of electroluminescent devices, but also inhibiting nonradiation energy loss for high efficiency. Besides emitting dopants, deuterated hosts have started to get studied also. Adachi et al. showed that a deuterated host material could realize a over two-time longer lifetime for green TADF device, due to the better morphological stability in the deuterated film . Additionally, Tang and colleagues observed a correlation between the kinetic isotope effect of the photodegradation reactions and the enhancement in device lifetime through the simultaneous deuteration of the hole-transporting material and host material, realizing up to an eight-fold increase in LT90 of conventional fluorescent blue device . Though the exact mechanism is still debating and complex, those preliminary works have evidenced the great potential of deuteration strategy. It is thus wondering if deuteration could address the instability issue of deep-blue PhOLEDs. Particularly, considering the highly needs on stable wide-energy-gap host, we here envisioned that the deuterated exciplex-forming host may further unlock the potential of deep-blue PhOLEDs, which, nevertheless, needs to be experimentally proved. And the underlying physics of deuterated exciplex still need to be explored as no similar study reported in literature.