We have previously demonstrated that DFT methods are not appropriate for accurately predicting the excited state properties of MR-TADF materials. Explicit inclusion of secondorder electronic correlation effects using wavefunction-based methods such as Spin component Scaling second-order approximate Coupled-Cluster (SCS-CC2) calculations with the cc-pVDZ basis set addresses this problem, resulting in accurate DEST prediction for MR-TADF materials. The two isomers possess identical S1 and T1 energies of 2.93 eV and 2.69 eV, respectively, and thus a DEST of 0.24 eV (Figure ), which is similar to previously reported ketone-containing MR-TADF materials. Compared to the parent compound DiKTa (DEST = 0.27 eV and S1 = 3.45 eV), there is a modest decrease in DEST and significant stabilization of S1. The smaller computed DEST in Sym-DiDiKTa to Asym-DiDIKTa relative to DiKTa is due to the increase in the π conjugation of these materials compared to DiKTa resulting in a lowering of the exchange energy, as has been documented in other extended MR-TADF systems, such as v-DABNA and OAB-ABP-1. The predicted stabilization of S1 results from the nitrogen atoms being positioned para to each other, which positively reinforce their electron-donating character, as has been previously reported. The oscillator strength associated with the S0-S1 transition is significant at 0.26 and 0.27 for Sym-DiDiKTa and Asym-DiDIKTa, respectively. The difference density pictures of S1 and T1 of each emitter highlight the alternating pattern of increasing and decreasing electronic density on neighbouring atoms that produce the emissive short-range charge transfer (SRCT) excited state, which is characteristic of MR-TADF materials. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) recorded in degassed dichloromethane (Figures and) document a reversible reduction wave at Ered = -0.96 and -0.94 V vs SCE for Sym-DiDiKTa and Asym-DiDiKTa, respectively. The oxidation wave of Sym-DiDiKTa is more reversible than that of Asym-DiDiKTa (both at 1.53 V vs SCE), revealing the impact of the regiochemistry that the tert-butyl groups play in terms of electrochemical stability. The corresponding HOMO and LUMO levels are nearly identical, at -5.87 eV for both compounds and -3.38 eV for Sym-DiDiKTa and -3.40 eV for Asym-DiDiKTa, respectively, which align well with the gas-phase DFT calculations at the PBE0/6-31G(d,p) level of theory (-5.94 eV and -2.69 eV, respectively, Table and Figure ). The experimentally determined HOMO levels of Sym-DiDiKTa and Asym-DiDiKTa are similar to that of DiKTa (-5.93 eV), while the LUMO levels are significantly stabilized (LUMO of DiKTa = -3.11 eV). The electrochemical data are summarized in Table . The monomolecular photophysical properties of Sym-DiDiKTa and Asym-DiDiKTa were first studied in dilute toluene solution (Figures and). The UV-vis absorption spectra of both emitters in toluene are expectedly nearly identical, yet show significant differences compared to that of DiKTa in terms of the SRCT absorption band's wavelength (around 435 for DiKTa but around 515 nm for Sym-DiDiKTa and Asym-DiDiKTa). The molar absorptivity, e, of the SRCT band for Sym-DiDiKTa and Asym-DiDiKTa is 26,325 M -1 cm -1 and 23,458 M -1 cm -1 , respectively, assigned to the transition to S1 according to the SCS-CC2 calculations (Figure ). The e is somewhat larger than reported for DiKTa (e of DiKTa = 21,000 M -1 cm -1 ), which is consistent with the trends in the calculated oscillator strength where f = 0.20 for DiKTa, compared to 0.26 and 0.27 for Sym-DiDiKTa and Asym-DiDiKTa, respectively. The absorption spectra of both Sym-DiDiKTa and Asym-DiDiKTa also show a high-energy shoulder at 485 nm (e = 11,680 and 10,238 M -1 cm -1 for Sym-DiDiKTa and Asym-DiDiKTa, respectively), which likely originates from a vibronic band and not a transition to a higher-lying singlet state given that computed energies of the S2 state in each of these two compounds is ca. 0.48 eV higher in energy and the S0-S2 transition possesses negligible oscillator strength. There is also a high-energy, high-intensity band at 373 nm (e = 31,900 M -1 cm -1 and 28,527 M -1 cm -1 for Sym-DiDiKTa and Asym-DiDiKTa, respectively, Figures and), which is assigned to transitions to S4 and S5, for Sym-DiDiKTa and Asym-DiDiKTa, respectively (Table ) based on the comparison with the SCS-CC2 simulated absorption spectra (Figure and Table ). The difference density plots of these states (Figure ) show that there is only minimal density situated on the central phenyl ring and more density situated on the carbonyl groups compared with the difference density pattern of the S1 state (vide supra.).