As shown in Figure , the distributions of the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) in the four emitters are mainly located over the whole DtBuCzB core, and extending to a small degree onto the fused benzothiophene moieties. Specifically, the natural transition orbital (NTO) analysis for the S1/T1 states of the four emitters, derived from the TDA-DFT calculations, reveals that for tDPABT1B and tCzBT1B, the sulfur atoms are only involved in the lowest unoccupied natural transition orbitals (LUNTOs). In contrast, the sulfur atoms in tDPABT2B and tCzBT2B participate solely in the highest occupied natural transition orbitals (HONTOs) (Figure ).