We modelled the electron density distribution in DiKTa-OBuIm and DiKTa-DPA-OBuIm by Density Functional Theory (DFT) calculations in the ground state, which we did at the PBE0/6-31G(d,p) level of theory in the gas phase (Figure ). Compared to DiKTa (HOMO = -6.20 eV, LUMO = -2.23 eV, ΔEg = 3.97 eV), both emitters possess a smaller HOMO-LUMO gap. The HOMO is more strongly affected by the incorporation of donor units. For instance, in the case of Cz-DiKTa and DMAC-DiKTa the HOMO is destabilized by 0.47 eV and 0.94 eV, respectively, compared to DiKTa. The lowest unoccupied molecular orbital (LUMO) for both compounds is localized on the DiKTa core (Figure ). This orbital is only slightly stabilized in DiKTa-DPA-OBuIm due to the presence of the more strongly electron-donating DPA group. The highest occupied molecular orbital (HOMO) in DiKTa-OBuIm is also localized on the DiKTa core and the electron density distribution of this molecule is reminiscent to that of a MR-TADF compound and is nearly identical to that of the parent emitter, DiKTa (Figure ). There is a very large change in both the electron density distribution and the HOMO energy between the two emitters. For DiKTa-DPA-OBuIm, the HOMO is mainly localized on the DPA unit but with some delocalization onto to the DiKTa core, resulting in a destabilization of this orbital from -5.91 eV in DiKTa-OBuIm to -5.19 eV in DiKTa-DPA-OBuIm. The HOMO-LUMO gap, DEg, thus decreases to 3.08 eV compared to that of DiKTa-OBuIm (3.74 eV). The excited states were modelled using spin-component scaling second-order approximate coupled-cluster (SCS-CC2) in tandem with the cc-pVDZ basis set (Table ). Figure shows the difference density plots for singlet (S) and triplet (T) excited states for DiKTa-OBuIm and DiKTa-DPA-OBuIm. Compared to DiKTa (S1 = 3.45 eV, T1 = 3.18 eV, f = 0.20, ΔEST = 0.27 eV), the lowest-lying singlet (S1) and triplet (T1) states are stabilized in the case of DiKTa-OBuIm, while the singlet-triplet energy gap, ΔEST, remained the same at 0.27 eV. The nature of S1 and T1 resemble to those of its parent DiKTa and so this compound is likely to behave as a MR-TADF emitter. The nature of the S2 state is n-π* in DiKTa-OBuIm. The excited state picture of DiKTa-DPA-OBuIm is different to that of other reported D-A type systems containing DiKTa as the acceptor. Long range charge transfer is not apparent here and instead the coupled cluster calculations predict a compound that is MR-TADF but where the electron density distribution is delocalized over the entire molecule. Compared to DiKTa-OBuIm, both S1 and T1 of DiKTa-DPA-OBuIm are stabilized to 3.07 eV and 2.83 eV, respectively. The ΔEST decreases to 0.24 eV and there is no intermediate triplet state. The trend of stabilized S1 and T1 states when a donor group decorates the DiKTa core (S1 = 3.45 eV, T1 = 3.18 eV) has been previously observed in reported emitters such as Cz-DiKTa (S1 = 3.35 eV, T1 = 3.09 eV) and DMAC-DiKTa (S1 = 3.43 eV, T1 = 3.17 eV). We also calculated the charge transfer character of each excited state, focussing on the distance of charge transfer (DCT). When considering the S1 excited state, there is an increase in CT character moving from DiKTa, DiKTa-OBuIm and DiKTa-DPA-OBuIm (DCT = 1.45 Å, 1.81 Å and 3.34 Å respectively) reflected in the increased donor strength. The electrochemical properties of DiKTa-OBuIm and DiKTa-DPA-OBuIm were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in acetonitrile with 0.1 M tetra-nbutylammonium hexafluorophosphate as the supporting electrolyte (Figure and Table ). The oxidation and reduction of both emitters showed good reversibility, which is beneficial for better performance in LEEC devices. The oxidation potentials, Eox, determined from the peak value of the first DPV curve are 1.05 V and 0.44 V for DiKTa-OBuIm and DiKTa-DPA-OBuIm, respectively, which correspond to HOMO energy levels of -5.85 eV and -5. Figure shows the solution-state photophysical properties of DiKTa-OBuIm and DiKTa-DPA-OBuIm in acetonitrile and the data are compiled in Table . The lowest energy absorption band for DiKTa-OBuIm at 453 nm (e = 17 × 10 3 M -1 cm -1 ) is red-shifted and slightly more intense than that of the parent DiKTa at 436 nm, (e = 14 × 10 3 M -1 cm -1 ) 26 owing to the increased conjugation in DiKTa-OBuIm. For the emitter 7a (Figure ) reported by Yan et al. the red-shift of the lowest energy absorption band was more pronounced than that in DiKTa-OBuIm. This band is assigned to a short-range charge transfer transition (SRCT) that is a hallmark characteristic in MR-TADF compounds. The Stokes shift is 54 nm (2361 cm -1 ) for DiKTa-OBuIm. The lowest energy absorption band in DiKTa-DPA-OBuIm is red-shifted and less intense (e = 6 × 10 3 M -1 cm -1 ) compared to DiKTa-OBuIm, in line with its decreased oscillator strength (vide supra.). According to the calculations (vide supra), the S1 excited state is also SRCT, but with larger LRCT content. Owing to the relative flexibility around the DPA donor unit, the Stokes shift is larger at 75 nm (2761 cm -1 ). DiKTa-OBuIm and DiKTa-DPA-OBuIm exhibited broad green (λPL = 507 nm, FWHM = 75 nm) and red (λPL = 563 nm, FWHM = 92 nm) emissions in MeCN, respectively. which is larger than DiKTa (46 nm in MeCN) in line with the greater LRCT character for these emitters, this observation has been noted for other donor decorated MR-TADF emitters. The photoluminescence quantum yield, FPL, in MeCN for DiKTa-OBuIm is 48% which decreases in air to 34%. The emission is much weaker in DiKTa-DPA-OBuIm, reflecting both the smaller oscillator strength of the transition to S1 and the greater non-radiative decay due to the energy gap law (FPL = 11% and 7%under vacuum and in air, respectively) in MeCN. The S1 and T1 levels were measured from the onsets of fluorescence (2.66 eV) and phosphorescence spectra (2.41 eV) in 2-MeTHF glass at 77 K (Figure ). DiKTa-OBuIm possesses a ΔEST of 0.25 eV. Unfortunately, DiKTa-DPA-OBuIm was insoluble in 2-MeTHF and so the measurement could not be made. No delayed component was observed in MeCN solution under vacuum for either of the compounds (Figure ). Lowest energy absorbance band, Absorptivity (e) in parentheses (/ × 10 3 M -1 s -1 ). d Steady-state emission maximum at 300 K. lexc = 340 nm. e Full width at half maximum of the emission peak. f S1 and T1 energies were obtained from the onsets of the respective prompt fluorescence (delay: 1 ns; gate time: 100 ns) and phosphorescence spectra (delay: 1 ms; gate time: 9 ms) at 77 K. λexc = 343 nm. g DEST = E(S1) -E(T1). h ΦPL in solutions were measured by the relative method using quinine sulfate as a standard (Φr = 54.6% in 1 N H2SO4), while absolute ΦPL of thin films were measured using an integrating sphere. lexc = 340 nm and the values in parentheses are in the presence of O2. i Prompt and delayed lifetimes in solutions and thin films obtained by TCSPC and MCS. λexc = 379 nm. j Intersystem and reverse intersystem crossing rates were calculated using the steady-state approximation method as described in literature. The thin film PL behavior of both emitters was then assessed in 1 wt% doped film in 1,3-di-9-carbazolylbenzene (mCP). At this doping concentration, the photophysical properties should reflect monomolecular entities. Emission was observed at 500 nm (FWHM = 66 nm) and 578 nm (FWHM = 95 nm)