Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, 100190 Beijing, China.
J Chem Phys. 2011 Sep 14;135(10):104703. doi: 10.1063/1.3632105.
Chemical substitutions are powerful molecular design tools to enhance the performance of organic semiconductors, for instance, to improve solubility, intermolecular stacking, or film quality. However, at the microscopic level, substitutions in general tend to increase the molecular reorganization energy and thus decrease the intrinsic charge-carrier mobility. Through density functional theory calculations, we elucidate strategies that could be followed to reduce the reorganization energy upon chemical substitution. Specific examples are given here for hole-transport materials including indolo-carbazoles and several triarylamine derivatives. Through decomposition of the total reorganization energy into the internal coordinate space, we are able to identify the molecular segment that provides the most important contributions to the reorganization energy. It is found that when substitution reduces (enhances) the amplitude of the relevant frontier molecular orbital in that segment, the total reorganization energy decreases (increases). In particular, chlorination at appropriate positions can significantly reduce the reorganization energy. Several other substituents are shown to play a similar role, to a greater or lesser extent.
化学取代是增强有机半导体性能的强大分子设计工具，例如提高溶解性、分子间堆积或薄膜质量。然而，在微观水平上，取代通常会增加分子重组能，从而降低本征电荷载流子迁移率。通过密度泛函理论计算，我们阐明了可以在化学取代时降低重组能的策略。这里给出了空穴传输材料（包括吲哚咔唑和几种三芳胺衍生物）的具体示例。通过将总重组能分解到内部坐标空间，我们能够确定对重组能贡献最大的分子片段。结果发现，当取代降低（增加）该片段中相关前线分子轨道的幅度时，总重组能降低（增加）。特别地，在适当位置的氯化可以显著降低重组能。还显示出其他几个取代基在不同程度上起到类似的作用。
