Pyrazinacene conjugated polymers: a breakthrough in synthesis and unraveling the conjugation continuum
Pyrazinacene conjugated polymers: a breakthrough in synthesis and unraveling the conjugation continuum
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DOI：
10.1039/d3sc06552a
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发表时间：
2024-02-02
期刊：
影响因子：
8.4
通讯作者：
Gavvalapalli，Nagarjuna
中科院分区：
文献类型：
--
作者：
Hameed，Fatima;Maity，Arindam;Gavvalapalli，Nagarjuna
吡嗪并苯是新一代的N-杂并苯，代表了一类新的稳定的n型材料，能够接受一个以上的电子，并显示出有趣的功能，包括亲质子性，卤代变色和氧化还原变色。令人惊讶的是，尽管自发现以来已有世纪，但由于底物范围未知以及缺乏有助于缩聚的吡嗪并苯单体，尚未有关于吡嗪并苯共轭聚合物的报道。突破这些挑战，在这项工作中，我们报告了以前未发现的和高度令人垂涎的吡嗪并苯共轭聚合物的合成。为了理解并苯内和沿着聚合物主链的共轭延伸的复杂性，合成了一系列具有电子多样性的四种吡嗪并苯共轭聚合物。聚合物合成需要优化12步合成途径中的沿着几个合成步骤。所产生的吡嗪并苯单体不适用于涉及Pd或Cu催化剂的流行的缩合聚合。令人满意的是，单体与HgCl 2的无Pd和Cu的脱卤化氢聚合在室温下在几分钟内产生高分子量的有机金属共轭吡嗪并苯聚合物。汞（II）在聚合过程中发挥的双重作用，结合RHgCl（中间体）的自偶联，是成功聚合的核心。值得注意的是，中间体的自偶联挑战了逐步增长聚合通常所需的严格的化学计量平衡，并提供了一种新的合成策略，即使在单体化学计量不平衡的情况下也能产生高分子量的共轭聚合物。电化学研究和DFT-B3 LYP模拟的组合表明，与完全氧化的四氮杂蒽相比，还原的吡嗪环的存在通过金属中心促进并苯间π-共轭。共轭的扩展导致了ca。与单体相比，聚合物的还原电位低2 eV，使这些聚合物的LUMO能级与一些最知名的n型聚合物相当。此外，在吡嗪并苯聚合物中NH质子的存在下，显示出离子致变色性和红移的紫外-可见吸收最大值约。100 nm。这项工作不仅显示了一种方法来实现高度理想的和难以捉摸的吡嗪并苯共轭聚合物，但也铺平了道路的n型共轭聚合物，可以进行多电子还原库。
Pyrazinacenes are next generation N-heteroacenes and represent a novel class of stable n-type materials capable of accepting more than one electron and displaying intriguing features, including prototropism, halochromism, and redox chromism. Astonishingly, despite a century since their discovery, there have been no reports on the conjugated polymers of pyrazinacenes due to unknown substrate scope and lack of pyrazinacene monomers that are conducive to condensation polymerization. Breaking through these challenges, in this work, we report the synthesis of previously undiscovered and highly coveted conjugated polymers of pyrazinacenes. In order to understand the intricacies of conjugation extension within the acene and along the polymer backbone, a series of electronically diverse four pyrazinacene conjugated polymers were synthesized. Polymers synthesis required optimizing a few synthetic steps along the 12-step synthetic pathway. The generated pyrazinacene monomers are not amenable to the popular condensation polymerizations involving Pd or Cu catalysts. Gratifyingly, Pd and Cu free dehydrohalogenation polymerization of the monomer with HgCl2 resulted in high molecular weight organometallic conjugated pyrazinacene polymers within a few minutes at room temperature. The dual role played by the Hg(II) during the polymerization, combined with the self-coupling of the RHgCl (intermediate), is at the core of successful polymerization. Notably, the self-coupling of intermediates challenges the strict stoichiometric balance typically required for step-growth polymerization and offers a novel synthetic strategy to generate high molecular weight conjugated polymers even with imbalanced monomer stoichiometries. A combination of electrochemical studies and DFT-B3LYP simulations indicated that the presence of the reduced pyrazine ring promotes interacene π-conjugation through the metal center, in contrast to completely oxidized tetrazaazaanthracene. The extension of conjugation results in ca. 2 eV lower reduction potential for polymers compared to the monomer, placing the LUMO energy levels of these polymers on par with some of the best-known n-type polymers. Also, the presence of NH protons in the pyrazinacene polymers show ionochromism and red-shift UV-vis absorption maximum by ca. 100 nm. This work not only shows a way to realize highly desirable and elusive pyrazinacene conjugated polymers but also paves the way for a library of n-type conjugated polymers that can undergo multi-electron reduction.