Photochemically Mediated Polymerization of Molecular Furan and Pyridine: Synthesis of Nanothreads at Reduced Pressures
Photochemically Mediated Polymerization of Molecular Furan and Pyridine: Synthesis of Nanothreads at Reduced Pressures
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光化学介导的分子呋喃和吡啶聚合：减压合成纳米线
DOI：
10.1021/jacs.2c09204
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发表时间：
2022
影响因子：
15
通讯作者：
Lopez, Steven A.
中科院分区：
文献类型：
--
作者：
Oburn, Shalisa M.;Huss, Steven;Cox, Jordan;Gerthoffer, Margaret C.;Wu, Sikai;Biswas, Arani;Murphy, Morgan;Crespi, Vincent H.;Badding, John V.;Lopez, Steven A.
纳米线是新兴的一维sp3杂化材料，具有高的预测拉伸强度和可调的带隙。它们可以通过将芳香族或非芳香族小分子压缩到15-30 GPa的压力来合成。最近，正在寻求降低提供纳米线所需的压力的新途径;焦点已经放在具有降低的芳香性、有利的堆叠和/或使用较高反应温度的分子的聚合上。在此，我们报告了吡啶和呋喃芳香族前体的光化学介导的聚合，其在减压下实现了纳米线的形成。在吡啶的情况下，发现缓慢压缩/解压缩与宽带UV光暴露的组合产生了结晶产物，其特征在于具有与先前在减压下合成的吡啶衍生的纳米线相似的晶面间距的六重衍射图案。当呋喃被压缩到8 GPa并暴露于宽带UV光时，回收结晶固体，其类似地展示具有类似于高压合成的呋喃衍生的纳米线的晶面间距的X射线衍射。我们的方法实现了提供呋喃衍生的纳米线所需的最大压力的1.9倍降低和吡啶衍生的纳米线所需的压力的1.4倍降低。密度泛函理论和多组态波函数为基础的计算被用来了解呋喃和随后的级联热环加成的光化学活化。起始压力的降低是由初始的[4+4]环加成，然后在聚合过程中越来越容易的热[4+2]-环加成引起的。
Nanothreads are emerging one-dimensional sp3-hybridized materials with high predicted tensile strength and a tunable band gap. They can be synthesized by compressing aromatic or nonaromatic small molecules to pressures ranging from 15–30 GPa. Recently, new avenues are being sought that reduce the pressure required to afford nanothreads; the focus has been placed on the polymerization of molecules with reduced aromaticity, favorable stacking, and/or the use of higher reaction temperatures. Herein, we report the photochemically mediated polymerization of pyridine and furan aromatic precursors, which achieves nanothread formation at reduced pressures. In the case of pyridine, it was found that a combination of slow compression/decompression with broadband UV light exposure yielded a crystalline product featuring a six-fold diffraction pattern with similar interplanar spacings to previously synthesized pyridine-derived nanothreads at a reduced pressure. When furan is compressed to 8 GPa and exposed to broadband UV light, a crystalline solid is recovered that similarly demonstrates X-ray diffraction with an interplanar spacing akin to that of the high-pressure synthesized furan-derived nanothreads. Our method realizes a 1.9-fold reduction in the maximum pressure required to afford furan-derived nanothreads and a 1.4-fold reduction in pressure required for pyridine-derived nanothreads. Density functional theory and multiconfigurational wavefunction-based computations were used to understand the photochemical activation of furan and subsequent cascade thermal cycloadditions. The reduction of the onset pressure is caused by an initial [4+4] cycloaddition followed by increasingly facile thermal [4+2]-cycloadditions during polymerization.