Lee Geon Hyeong, Kim Young Sik
J Nanosci Nanotechnol. 2018 Oct 1;18(10):7211-7215. doi: 10.1166/jnn.2018.15481.
Novel thermally activated delayed fluorescence (TADF) materials with pyridine (Pd), pyrimidine (Pm), and triazine (Trz) as electron acceptors and carbazole (Cz) as an electron donor (TmCzPd, TmCzPm, and TmCzTrz) were designed, and the effect of the number of nitrogen (N) atoms with acceptor units was investigated by comparing their electronic and optical properties for blue organic light-emitting diodes (OLEDs). Using density functional theory (DFT) and time-dependent DFT calculations, we obtained the electron distributions of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), and the energies of the lowest singlet (S1)and lowest triplet (T1) excited states. The calculated energy difference (ΔEST) between the S1 and T1 states of TmCzPm (0.200 eV) and TmCzTrz (0.186 eV) were smaller than that of TmCzPd (0.395 eV). We show that TmCzPm would be a suitable blue OLED emitter because it has sufficiently small ΔEST values, which is favorable for a reverse intersystem crossing process from the T1 to S1 states, and an emission wavelength of 473.1 nm with sufficiently large oscillator strength for fluorescence.
设计了以吡啶（Pd）、嘧啶（Pm）和三嗪（Trz）作为电子受体、咔唑（Cz）作为电子供体的新型热激活延迟荧光（TADF）材料（TmCzPd、TmCzPm和TmCzTrz），并通过比较它们在蓝色有机发光二极管（OLED）中的电子和光学性质，研究了带有受体单元的氮（N）原子数量的影响。使用密度泛函理论（DFT）和含时DFT计算，我们获得了最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）的电子分布，以及最低单重态（S1）和最低三重态（T1）激发态的能量。TmCzPm（0.200 eV）和TmCzTrz（0.186 eV）的S1和T1态之间的计算能量差（ΔEST）小于TmCzPd（0.395 eV）。我们表明，TmCzPm将是一种合适的蓝色OLED发光体，因为它具有足够小的ΔEST值，这有利于从T1态到S1态的反向系间窜越过程，并且发射波长为473.1 nm，具有足够大的荧光振子强度。
