Aromatic polyimides (PIs) exhibit excellent mechanical and thermal properties due to the charge transfer (CT) interactions. The introduction of benzimidazole with hydrogen interactions is a notably effective strategy for yielding exceptional superheat resistance and high thermal dimensional stability of PIs. Decoupling the stacking behavior under CT interactions and hydrogen interactions is crucial for elucidating the behavior of PIs macromolecules. Herein, the packing structure of PIs guided by hydrogen interactions was visualized using three plausible model compounds and theoretical simulations. The phthalimide fragment exhibited a preference for anti-parallel offset stack π-π stacking, while the phenylbenzimidazole fragment formed a shoulder-to-shoulder arrangement, resulting in the adoption of a Mixed Layer Packing (MPL) conformation, which is not the common Preferred Layer Packing (PLP) conformation. The CT interactions of phthalimide served as the primary stacking driving force, rather than the hydrogen interaction of benzimidazole. The intrinsic nature of packing behavior was that the minima and maxima parts of the electron density deviated from the midperpendicular of benzene and succinimide, where the LOL-π map, ESP map and SAPT calculations provided insights into the microscopic electronic structure. Finally, experimental PI fibers was prepared and their XRD pattern further confirmed the presence of an anti-parallel offset π-π stack conformation.

中文翻译：

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揭示含苯并咪唑聚酰亚胺的堆积结构：反平行偏移π-π堆积

由于电荷转移 (CT) 相互作用，芳香族聚酰亚胺 (PI) 表现出优异的机械和热性能。引入具有氢相互作用的苯并咪唑是一种非常有效的策略，可以使 PI 具有优异的过热稳定性和高热尺寸稳定性。解耦 CT 相互作用和氢相互作用下的堆积行为对于阐明 PI 大分子的行为至关重要。在此，利用三种合理的模型化合物和理论模拟，将氢相互作用引导的 PI 堆积结构可视化。邻苯二甲酰亚胺片段表现出对反平行偏移堆叠π-π堆叠的偏好，而苯基苯并咪唑片段形成肩对肩排列，导致采用混合层堆积（MPL）构象，这不是常见的首选构象层包装 (PLP) 构象。邻苯二甲酰亚胺的 CT 相互作用是主要的堆积驱动力，而不是苯并咪唑的氢相互作用。堆积行为的本质是电子密度的最小值和最大值部分偏离苯和琥珀酰亚胺的中垂线，其中LOL-π图、ESP图和SAPT计算提供了对微观电子结构的洞察。最后，制备了实验性PI纤维，其XRD图谱进一步证实了反平行偏移π-π堆叠构象的存在。