for DM-BD1 and 25 o for DM-BD2 from the crystal structures, where the not quite co-facial orientation has been demonstrated by Kaji et al. to be critical to turn on spin-orbit coupling and facilitate RISC. Interestingly, both compounds showed broad, structureless CT emission Reproduced with permission. To enhance the D-A electronic interactions by adjusting the D-A distance, Zhang et al. employed a xanthene bridge in two TSCT TADF emitters, mCz-Xo-TRZ and dCz-Xo-TRZ (Figure ), that possess space-confined face-to-face D-A alignment and minimized D-A distance down to 2.7-2.8 Å, which is shorter than twice the van der Waals radius of a carbon atom (1.7 Å). As a result, the greatly strengthened electronic interaction between D and A lead to fast kr of 9.9 and 8.7 ´10 6 s -1 for mCz-Xo-TRZ and dCz-Xo-TRZ, respectively. The stronger donor in dCz-Xo-TRZ versus mCz-Xo-TRZ leads to a red-shift of the PL spectrum in toluene (from 454 nm to 461 nm) and the 30 wt% doped film in bis(diphenylphosphinyl)-dibenzofuran (PPF) matrix (from 469 nm to 482 nm,). The FPL values of 90% and 92% for mCz-Xo-TRZ and dCz-Xo-TRZ, respectively, are high; however, the kRISC values are 3.0×10 5 s -1 and 3.3×10 Reproduced with permission. Copyright © 2021, American Chemical Society.