High-Efficiency Diphenylsulfon Derivative-Based Organic Light-Emitting Diode Exhibiting Thermally-Activated Delayed Fluorescence

A novel thermally-activated delayed fluorescence (TADF) material with diphenyl sulfone (DPS) as an electron acceptor and 3,6-dimethoxycarbazole (DMOC) and 1,3,6,8-Tetramethyl-9H-carbazole (TMC) as electron donors was investigated theoretically for a blue organic light emitting diode (OLED) emitter. We calculated the energies of the first singlet (S1) and the first triplet (T1) excited states of the TADF materials by using the dependence on the charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT to perform density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the ground state. The calculated EST value, where EST is the difference in energy between the S1 and T1 states, of TMC-DPS (0.094 eV) was smaller than DMOC-DPS (0.386 eV) because of the large dihedral angles between the donor and the accepter moieties. We show that TMC-DPS would be a suitable blue OLED emitter because it has a large dihedral angle that creates a small spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO), consequently, it has a small value of EST and an emission wavelength of 2.82 eV and 439.9 nm, respectively.