Diphenylsulphone-Based Highly Efficient Blue Thermally Activated Delayed-Fluorescence Emitter

A novel thermally activated delayed-fluorescence (TADF) material (2BDPCC-DPS) using 3,6-bis(3,6-diphenylcarbazolyl) carbazole (BDPCC) as an electron donor and diphenylsulphone (DPS) as an electron acceptor was designed and the electronic and optical properties were theoretically investigated for a blue organic light-emitting diode (OLED) emitter. Using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, we attained the electron distribution of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and the energy of the lowest singlet (S-1) and the lowest triplet (T-1) excited states; the HOMO and the LUMO are located over the BDPCC and the DPS units, respectively. The large separation between the HOMO and LUMO then provides a small energy difference (Delta E-ST) between the S-1 and T-1 states. For the HOMO on the BDPCC unit, the bis(3,6-diphenylcarbazole) components of the BDPCC unit act as weak electron-donating units for the carbazole attached to the DPS unit. As a result, the HOMO of 2BDPCC-DPS is largely delocalized over the whole BDPCC unit, thus considerably enhancing the rate of radiative decay by inducing a large oscillator strength (F) for fluorescence, even when a small overlap exists between the HOMO and LUMO. The 2BDPCC-DPS would thus provide highly efficient TADF properties with both high F and low Delta E-ST for the blue OLED emitter.