In agreement with what is intuitive upon visual inspection of the NTOs (Figure and), the S1 state of 2 is assigned as CT in nature. The electron-hole analysis for T1 is near-identical to that of S1, meaning both states are the same in configuration (CT) with the same spatial distribution. Hence, as expected from El-Sayed's rule the calculated S1-T1 SOCME is very small (0.05 cm -1 ), and rISC should be very inefficient between these states. A similar case is observed for the S1 and T1 states of 1 (Table It has been accepted that in TADF materials vibronic coupling can facilitate rISC between a CT singlet such as S1 and upper LE triplet states, for which there should be greater SOC due to a change in excited state configuration. 3,6,8-10 Indeed, the SOCME values between S1 and upper LE triplet states (T3 for 1; T13, T14 and T15 for 2) are on the order of 0.1-0.25 cm -1 .