The ground-state geometries of the four emitters were optimized using density functional theory (DFT) at level of PBE0/6-31G (d,p) level of theory in the gas phase, where the starting geometries of tDPABT1B and tCzBT2B was taken from their X-ray crystal structures, and for tDPABT2B and tCzBT1B from the MM2-optimized geometries. Time-dependent DFT calculations within the Tamm-Dancoff approximation (TDA-DFT) were employed to optimize the geometries of S1/T1