Benzofuropyridine-Based Highly Efficient Thermally Activated Delayed Fluorescence Emitters

Novel thermally activated delayed fluorescence (TADF) materials with benzofuro[2,3-b] pyridine (BFPd) as an electron acceptor and carbazole derivatives [carbazole (Cz), 1,3,6,8-tetramethyl-9H-carbazole (tmCz), and 9'H-9,3': 6',9''-tercarbazole (terCz)] as electron donors are designed, and their electronic and optical properties are investigated theoretically for a deep blue organic light-emitting diode (OLED). We obtain the energies of the first singlet (S-1) and first triplet (T-1) excited states of TADF materials by performing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the ground state by using the dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. We show that terCz-BFPd would be a suitable blue OLED emitter because it has sufficiently small Delta E-ST value (0.048 eV), which is favorable for a reverse intersystem crossing process from the T-1 to S-1 states and an emission wavelength of 432.8 nm with sufficiently large oscillator strength (F) value.