The ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) spectra at both room temperature and 77 K in dilute toluene solution are shown in Fig. . D-SiCzCz and D-SiTrzCz2 exhibited intense absorption bands between 300 and 360 nm, which were assigned to the π-π* transition absorption. Both deuterated compounds featured broad structureless emission bands with peak values at 372 and 431 nm, which exhibited a significant red-shift in comparison with those of their protonated counterparts, with values of 360 and 380 nm, respectively . The singlet and triplet energies of D-SiCzCz and D-SiTrzCz2 estimated from the onset point of the fluorescence and phosphorescence spectra were 3.51/3.09 and 3.29/3.06 eV, respectively. These values were similar to those of the non-deuterated compounds. Their absorption and emission curves in film state also exhibited no significant difference with contrast molecules (Supplementary Fig. and Supplementary Table ). As shown in Fig. , the emission of D-SiCzCz: D-SiTrzCz2 and SiCzCz: SiTrzCz2 mixtures were both located at 466 nm, exhibiting an obvious red-shifted trend in contrast to their respective constituent components (D-SiCzCz: 377 nm, D-SiTrzCz2: 427 nm, SiCzCz: 387 nm and SiTrzCz2: 428 nm), indicating their emissions should be from the exciplexes. Such exciplex formation could also be confirmed by analysing the transient PL decay of the mixtures, as shown in Supplementary Fig. . It was observed that the deuterated exciplex exhibited a prolonged lifetime with a delayed component of 648.8 ns (Supplementary Table ), which is considerably longer than the nanosecond lifetime of the individual components. Meanwhile, the triplet energies of the exciplexes were measured to be 2.95 and 2.90 eV for deuterated and nondeuterated mixtures, respectively (Supplementary Fig. ). These results suggest that deuteration has a negligible effect on the energy levels involved in the radiative processes. To investigate the effect of deuteration on the intrinsic photostability of the exciplex-forming host materials, we performed PL stability test of the protonated and deuterated mixtures in vacuumevaporated films (with thickness of 100 nm) by continuous ultraviolet irradiation with a peak wavelength of 360 nm (Fig. and Supplementary Fig. ). Apparently, the shape of the emission bands remains unchanged, but the proportion generally declined to a lesser extent with the extension of the exposure time. The relative intensity decreased from 100% to 93% and 86% for D-SiCzCz: D-SiTrzCz2 and SiCzCz: SiTrzCz2 mixtures, indicating a positive deuteration effect on the photostability of the host materials . To find out the deuterated host influence on the photophysical properties of the dopant, we fabricated the doped films using 10 wt% BD-02 as the emitter, where BD-02 stands for