Study of Phenoxaborin Derivatives for Thermally Activated Delayed Fluorescence Emitters.

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 (S1) and the lowest triplet (T1) excited states. Values for the calculated energy difference between the S1 state and the T1 state (ΔEST) 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 ΔEST values, which is favorable for a reverse intersystem crossing process (RISC) from the T1 to the S1 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 (ΔEST) between the S1 state and the T1 state and a large F for the OLED.