Hasegawa Tsukasa, Ashizawa Minoru, Kawauchi Susumu, Masunaga Hiroyasu, Ohta Noboru, Matsumoto Hidetoshi
Department of Materials Science and Engineering, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku Tokyo 152-8552 Japan
Department of Chemical Science and Engineering, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku Tokyo 152-8552 Japan.
RSC Adv. 2019 Apr 8;9(19):10807-10813. doi: 10.1039/c9ra02413a. eCollection 2019 Apr 3.
The quinoxalineimide (QI) unit, containing the electron-withdrawing quinoxaline and imide groups, is an electron-deficient building block for organic semiconductor materials. In this study, three fluorinated or chlorinated QIs (QI-1F, QI-2F, and QI-2Cl), have been designed and developed. We report the impact of the fluorination or chlorination of the QI unit on the electronic structures and charge carrier transport properties as compared to unsubstituted QI (QI-2H) bearing the same -hexyl side chains. The frontier molecular orbital energy levels downshifted with the incorporation of fluorine or chlorine atoms onto the π-framework of QI. Single-crystal structure analyses revealed that all QI-based molecules have an entirely planar backbone and are packed into two-dimensional slipped stacks with diagonal electronic coupling that enables two-dimensional charge carrier transport. Notably, the doubly fluorinated or chlorinated QIs formed compact molecular packing in the single-crystal structures through an infinite intermolecular network relative to unsubstituted QI (QI-2H). The field-effect transistor-based QI molecules exhibited typical n-channel transport properties. As compared to unsubstituted QI (QI-2H), the chlorinated QI exhibited improved electron mobilities up to 7.1 × 10 cm V s. The threshold voltages of the fluorinated or chlorinated QI devices were clearly smaller than that of QI-2H, which reflects the lowest unoccupied molecular orbital levels of the molecules. This study demonstrates that the fluorinated or chlorinated QIs are versatile building blocks in creating n-channel organic semiconductor materials.
喹喔啉二酰亚胺（QI）单元含有吸电子的喹喔啉和酰亚胺基团，是有机半导体材料的缺电子结构单元。在本研究中，设计并开发了三种氟化或氯化的QI（QI-1F、QI-2F和QI-2Cl）。我们报告了与带有相同己基侧链的未取代QI（QI-2H）相比，QI单元的氟化或氯化对电子结构和电荷载流子传输性质的影响。随着氟或氯原子引入到QI的π骨架上，前沿分子轨道能级下移。单晶结构分析表明，所有基于QI的分子都有完全平面的主链，并堆积成具有对角电子耦合的二维滑移堆叠，从而实现二维电荷载流子传输。值得注意的是，相对于未取代的QI（QI-2H），双氟化或氯化的QI在单晶结构中通过无限分子间网络形成紧密的分子堆积。基于场效应晶体管的QI分子表现出典型的n沟道传输性质。与未取代的QI（QI-2H）相比，氯化QI的电子迁移率提高到7.1×10 cm V s。氟化或氯化QI器件的阈值电压明显小于QI-2H的阈值电压，这反映了分子的最低未占据分子轨道能级。本研究表明，氟化或氯化的QI是制备n沟道有机半导体材料的通用结构单元。
