Novel thermally activated delayed fluorescence (TADF) emitters were designed with diphenylsulfone (DPS) as an electron acceptor and carbazole derivatives as electron donors and their electronic and optical properties were investigated theoretically for applications to blue organic light-emitting diodes (OLEDs). By using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, we obtained the electron distributions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) as well as the energy of the lowest singlet (S-1) and lowest triplet (T-1) excited states. We show that 2mDTC-DPS would be a suitable blue OLED emitter because it has sufficiently small ?E-ST value, which is favorable for a reverse intersystem crossing (RISC) process from T-1 to S-1 states and an emission wavelength of 429?nm with sufficiently large F values.