Department of Chemistry, Imperial College London, White City Campus, London W12 0BZ, UK.
Phys Chem Chem Phys. 2019 Feb 27;21(9):5059-5067. doi: 10.1039/c8cp07603k.
The properties of an organic semiconductor are dependent on both the chemical structure of the molecule involved, and how it is arranged in the solid-state. It is challenging to extract the influence of each individual factor, as small changes in the molecular structure often dramatically change the crystal packing and hence solid-state structure. Here, we use calculations to explore the influence of the nitrogen position on the charge mobility of a chiral organic molecule when the crystal packing is kept constant. The transfer integrals for a series of enantiopure aza[6]helicene crystals sharing the same packing were analysed in order to identify the best supramolecular motifs to promote charge carrier mobility. The regioisomers considered differ only in the positioning of the nitrogen atom in the aromatic scaffold. The simulations showed that even this small change in the chemical structure has a strong effect on the charge transport in the crystal, leading to differences in charge mobility of up to one order of magnitude. Some aza[6]helicene isomers that were packed interlocked with each other showed high HOMO-HOMO integrals (up to 70 meV), whilst molecules arranged with translational symmetry generally afforded the highest LUMO-LUMO integrals (40-70 meV). As many of the results are not intuitively obvious, a computational approach provides additional insight into the design of new semiconducting organic materials.
有机半导体的性质既取决于所涉及分子的化学结构，也取决于其在固态中的排列方式。要提取每个单独因素的影响具有挑战性，因为分子结构的微小变化通常会极大地改变晶体堆积和固态结构。在这里，我们使用计算来探索当晶体堆积保持不变时，氮原子位置对手性有机分子电荷迁移率的影响。分析了一系列具有相同堆积方式的对映纯氮杂[6]螺旋烯晶体的转移积分，以确定最佳的超分子基序来促进电荷载流子迁移率。所考虑的区域异构体仅在芳构骨架中氮原子的定位上有所不同。模拟表明，即使化学结构发生这种微小变化，也会对晶体中的电荷输运产生强烈影响，导致电荷迁移率差异高达一个数量级。一些与彼此互锁的氮杂[6]螺旋烯异构体表现出高 HOMO-HOMO 积分（高达 70 meV），而具有平移对称性排列的分子通常提供最高的 LUMO-LUMO 积分（40-70 meV）。由于许多结果并不直观，因此计算方法为设计新的半导体有机材料提供了更多的见解。
