Departamento de Química Física, Universidad de Alicante, 03080 Alicante, Spain.
Departamento de Física Aplicada, Universidad de Alicante, 03080 Alicante, Spain.
Molecules. 2019 Feb 9;24(3):609. doi: 10.3390/molecules24030609.
The standard procedure to identify the hole- or electron-acceptor character of amorphous organic materials used in OLEDs is to look at the values of a pair of basic parameters, namely, the ionization potential (IP) and the electron affinity (EA). Recently, using published experimental data, the present authors showed that only IP matters, i.e., materials with IP > 5.7 (<5.7) showing electron (hole) acceptor character. Only three materials fail to obey this rule. This work reports ab initio calculations of IP and EA of those materials plus two materials that behave according to that rule, following a route which describes the organic material by means of a single molecule embedded in a polarizable continuum medium (PCM) characterized by a dielectric constant ε . PCM allows to approximately describe the extended character of the system. This "compound" system was treated within density functional theory (DFT) using several combinations of the functional/basis set. In the preset work ε was derived by assuming Koopmans' theorem to hold. Optimal ε values are in the range 4.4⁻5.0, close to what is expected for this material family. It was assumed that the optical gap corresponds to the excited state with a large oscillator strength among those with the lowest energies, calculated with time-dependent DFT. Calculated exciton energies were in the range 0.76⁻1.06 eV, and optical gaps varied from 3.37 up to 4.50 eV. The results are compared with experimental data.
确定用于 OLED 的非晶有机材料的空穴或电子受体特性的标准程序是查看一对基本参数的值，即电离势 (IP) 和电子亲和力 (EA)。最近，本作者使用已发表的实验数据表明，只有 IP 很重要，即 IP>5.7（<5.7）的材料具有电子（空穴）受体特性。只有三种材料不符合此规则。这项工作报告了这些材料的从头算 IP 和 EA 以及另外两种符合该规则的材料的计算结果，采用了一种通过单个分子嵌入具有介电常数 ε 的极化连续介质 (PCM) 来描述有机材料的方法。PCM 允许近似描述系统的扩展特性。该“化合物”系统在密度泛函理论 (DFT) 中使用几种功能/基组组合进行了处理。在本工作中，ε 是通过假设 Koopmans 定理成立来推导的。最佳 ε 值在 4.4⁻5.0 范围内，接近该材料家族的预期值。假设光学带隙对应于具有最低能量的激发态之一，该激发态具有较大的振子强度，通过时间相关的 DFT 计算得出。计算出的激子能量在 0.76⁻1.06 eV 范围内，光学带隙从 3.37 到 4.50 eV 不等。结果与实验数据进行了比较。
