To predict and rationalize the optoelectronic properties of the two emitters, density functional theory (DFT) modelling was first performed in the gas phase at the PBE0/6-31G(d,p) level (Figure ). The calculated energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are presented in Figures and The excited-state properties were calculated using time-dependent DFT (TD-DFT) with the Tamm-Dancoff approximation (TDA-DFT) based on the optimized ground-state geometries obtained at the same level of theory. As excepted, the S1 energy is stabilized from 2.32 eV in PhDPA-DiKTa to 2.25 eV in MeODPA-DiKTa, following the trend in the HOMO-LUMO gaps. The calculated T1 energies for PhDPA-DiKTa and MeODPA-DiKTa are 1.87 and 1.76 eV, respectively, resulting in similarly large ΔEST values of 0.49 and 0.47 eV, respectively. The overestimated ΔEST values originate from the use of TDA-DFT calculations, which do not account for multiple excitations. Due to the large molecular size of PhDPA-DiKTa and MeODPA-DiKTa, neither of the more accurate spin-SCS-CC2 or double hybrid calculations converged (Figure ). The S1 and T1 states are predicted to possess mainly short-range charge-transfer (SRCT) character located on the MR-TADF core (Figure ). The T2 states for both compounds have mainly long-range charge-transfer (LRCT) character and are also close in energy to the respective S1 states (PhDPA-DiKTa, S1/T22.32/2.30 eV) and MeODPA-DiKTa, (S1/T2=2.25/2.21 eV). This difference in the nature of S1 and T2 states will result in enhanced spin-orbit coupling (SOC) and assist in RISC following El Sayed's rules. As expected, the SOC matrix element (ξ(S1, T2) of 0.34 cm -1 for PhDPA-DiKTa, and 0.39 cm -1 for MeODPA-DiKTa) are much larger than those of ξ(S1, T1) of 0.29 cm -1 for PhDPA-DiKTa, and 0.19 cm -1 for MeODPA-DiKTa. So, the small energy gap together with the larger ξ(S1, T2) points to RISC proceeding via T2.