In this work, the chemical reduction of a hybrid pyracylene-hexa-peri-hexabenzocoronene (HPH) nanographene was investigated with different alkali metals (Na, K, Rb) to reveal its remarkable multielectron acceptor abilities. The UV–vis and ¹H NMR spectroscopy monitoring of the stepwise reduction reactions supports the existence of all intermediate reduction states up to the hexaanion for HPH. Tuning the experimental conditions enabled the synthesis of the HPH anions with gradually increasing reduction states (up to −5) isolated with different alkali metal ions as crystalline materials. The single-crystal X-ray diffraction structure analysis demonstrates that the highly negatively charged HPH anions (−4 and −5) exhibit a drastic geometry change from boat-shaped (observed in the neutral parent, mono- and dianions) to a chair conformation, which was proved to be fully reversible by NMR spectroscopy. DFT calculations show that this geometry change is induced by an enhanced interaction between the coordinated metal ions and negatively charged HPH core in the chair conformation.

中文翻译：

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揭开 π 膨胀吡啶的多电子受体特性：可逆的船椅转换


在这项工作中，研究了使用不同碱金属（Na、K、Rb）对杂化吡啶-六-六苯并晕（HPH）纳米石墨烯的化学还原，以揭示其显着的多电子受体能力。逐步还原反应的 UV-vis 和 ¹ H NMR 光谱监测支持 HPH 直至六阴离子的所有中间还原态的存在。调整实验条件使得能够合成具有逐渐增加的还原态（高达-5）的HPH阴离子，并与不同的碱金属离子作为晶体材料分离。单晶X射线衍射结构分析表明，带高负电荷的HPH阴离子（−4和−5）表现出从船形（在中性母体、单阴离子和双阴离子中观察到）到椅形构象的巨大几何变化，核磁共振波谱证明这是完全可逆的。 DFT 计算表明，这种几何变化是由椅子构象中配位金属离子和带负电的 HPH 核心之间增强的相互作用引起的。