were optimized using Density Functional Theory (DFT) at the PBE0 30 /6-31G(d,p) level 31 in the gas phase starting from a geometry generated in Chem3D. At the optimized S0 geometries The excited-state properties were calculated using time-dependent DFT (TD-DFT) within the Tamm-Dancoff approximation (TDA-DFT) based on the optimized ground-state geometries (Figure ). The oscillator strength, f, for the S0 → S1 transition of 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz is 0.06, 0.01, 0.10 and 0.08, respectively, reflecting the relatively smaller torsions and thus greater conjugation that exist between the position 3, 6 donors and the acceptor moieties in 2FBP2GCz and 2FBP2DPACz. The S1 energies are 2.09 eV for 2GCzBP, 1.95 eV for 2DPACzBP, 2.42 eV for 2FBP2GCz and 2.10 eV for 2FBP2DPACz, while the corresponding T1 energies are 2.04 eV, 1.87 eV, 2.32 eV and 2.02 eV, respectively, both following a similar trend to that observed for DEHOMO-LUMO values (Figure ). All four compounds have small predicted ΔEST of less than 0.10 eV, suggesting that these compounds should emit via TADF. There is a larger S1-T1 spin-orbital coupling matrix element, SOCME, in 2FBP2GCz (0.19 cm -1 ) and in 2GCzBP (0.10 cm -1 ) than that in 2FBP2DPACz (0.09 cm -1 ) and 2DPACzBP (0.06 cm -1 ) (Figure ), indicating that the ISC will likely be faster in 2FBP2GCz and 2GCzBP than that in the other two compounds. NTO analyses at the S0-optimized geometry (Figure ) demonstrated that the low-lying excited states in all four compounds possess charge transfer (CT) character. Holes and electrons are well separated on the donor and acceptor moieties, respectively. There is somewhat smaller separation in the T1 state of 2FBP2GCz and 2FBP2DPACz, so this state in these two compounds is better described as a mixture of locally-excited (LE) and CT character (Figure ). eV, -3.07 eV, -3.08 eV and -3.02 eV for 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz, respectively, and align with the trend found for the DFT calculations (Figure ). 2GCzBP and 2FBP2GCz both have two resolvable quasi-reversible oxidation waves, with similar first oxidation potentials at Eox of 1.03 V, and second oxidation potentials at 1.13 V, which correspond to the oxidation of the inner carbazole and the peripheral tert-butylcarbazole, respectively.