Study of Phenoxaborin Derivatives for Thermally Activated Delayed Fluorescence Emitters

Abstract

Novel thermally activated delayed fluorescence (TADF) materials including 10H-phenoxaborin (PXB) as an electron acceptor and carbazole derivatives [carbazole (Cz), 1-methyl-carbazole (1-m-Cz), and 3,6-bis(3,6-diphenylcarbazolyl) carbazole (BDPCC)] as electron donors (Cz-PXB, 1-m-Cz-PXB, and BDPCC-PXB) were designed and investigated theoretically for deep blue organic light-emitting diode (OLED). Using density functional theory (DFT) and time-dependent DFT calculations, we obtained the electron distribution of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and the energy of the lowest singlet (S-1) and the lowest triplet (T-1) excited states. Values for the calculated energy difference between the S-1 state and the T-1 state (Delta E-ST) of 1-m-Cz-PXB (0.158 eV) and BDPCC-PXB (0.058 eV) were smaller than for Cz-PXB (0.265 eV). Both materials had sufficiently small Delta E-ST values, which is favorable for a reverse intersystem crossing process (RISC) from the T-1 to the S-1 states. 1-m-Cz-PXB (0.1067) and BDPCC-PXB (0.0857) also have larger oscillator strengths (F) than reference material DMAC-PXB (0.0001). Our results showed that 1-m-Cz-PXB and BDPCC-PXB would have highly efficient TADF properties in terms of a small-enough energy difference (Delta E-ST) between the S-1 state and the T-1 state and a large F for the OLED.