were significantly longer than that of the 2B-DTACrs (13.1 μs). The estimated rate constants of radiative and nonradiative decays from S1 (kr, and knr, respectively), intersystem crossing (kISC), and kRISC are summarized in Table . The kRISC values for 1B-CzCrs and 2B-CzCrs are 3.36 and 0.41 ´ 10 3 s -1 , respectively; these are a two order difference with that of 2B-DTACrs (1.3 ´ 10 5 s -1 ). There is also a one-order difference in kRISC between 1B-CzCrs and 2B-CzCrs. To help explain this difference, spin-orbit coupling (SOC) magnitude was investigated with PBE0/6-31g(d,p) level of theory in the gas phase (Table ). The SOC value between T1 and S1 for 1B-CzCrs is 0.1187 cm -1 , a two-fold higher value compared with that of 2B-CzCrs (0.0592 cm -1 ). The SOC values between S1 and T2 also reflect this same trend at 0.0995 cm -1 and 0.060 cm -1 for 1B-CzCrs and 2B-CzCrs, respectively. This in itself explains the faster kRISC in 1B-CzCrs compared with 2B-CzCrs. Further, considering the energy splitting between S1-T1 and S1-T2 (0.33 and 0.12 eV for 1B-CzCrs, 0.40 and 0.08 eV for 2B-CzCrs, respectively), it is obvious why the asymmetric 1B-CzCrs has a faster kRISC than the symmetric 2B-CzCrs. From these results, the replacement of the diphenylamine by carbazole in this emitter design has both pros and cons, i.e., turning on TADF yet slowing kRISC. It is however noteworthy that the asymmetry in 1B-CzCrs leads to faster kRISC than in 2B-CzCrs while this was not the case with the 1B-DTACrs/2B-DTACrs family.