Polyyne and cumulene rotaxanes: Toward insulated molecular wires

由sp-杂化碳构成的低聚分子，即聚己烷和聚己烷，由于其独特的一维骨架而具有重要的基础意义。它们也是预测碳同素异形体碳炔性质的关键环节。在应用层面上，聚炔是分子线的理想候选材料，它们表现出令人印象深刻的非线性光学（NLO）特性，并且它们是富碳结构的宝贵基石。相反，由于已知衍生物的数量有限，积雨云作为共轭材料的潜力基本上尚未被探索。聚炔和累积烯的合成和化学目前依赖于相当小的反应工具箱，并且很少被证明广泛适用于扩展的聚炔和累积烯。然而，除了合成困难之外，由于聚炔和积云的不稳定性/反应性，还存在着重大挑战，这直接导致了这些独特分子在现实世界设备中的应用很少。本课题的研究旨在通过发展合成方法，形成通过机械键稳定的衍生物，即轮烷，来解决聚烯烃和积积烯的稳定性问题。由此形成的轮烷将为基础研究提供产品，也可用于纳米级器件。工作计划包括三个发现领域。首先，Work-Package 1将优化聚轮烷的合成方法，包括底物、反应条件、过渡金属催化剂、溶剂、大环组分的大小和功能。接下来，我们将努力评估和改进参数，以形成稳定的多炔，与裸的非轮烷类似物相比。最后这一点的成功结论将提供前所未有的长度多炔，以研究碳炔的性质。然后，工作包2探索可能附加到聚乙烯末端的塞子。这里的主要目标集中在形成功能化的聚烷轮烷。目标基团包括芳香族和杂芳香族，它们为金属或石墨烯电极提供分子线。或者，供体和受体（D-A）基团将连接以提供极化的推拉多炔。将研究D-A多烯与已知的D-A多烯的比较，以确定三键介导通信的效率，以及优化的NLO材料的形成。最后，为聚烷轮烷制定的协议将适用于形成累积烯轮烷（Work-Package 3）。迄今为止，超过100个积云的衍生物在溶液或固态中不够稳定。因此，提出的研究提供的化合物将首次有机会探测这类sp-碳低聚物的较长成员的性质。

Oligomeric molecules built from sp-hybridized carbon, namely polyynes and cumulenes, are fundamentally important due to their unique one-dimensional skeleton. They are also the key link to predicting the properties of the carbon allotrope carbyne. On an applied level, polyynes are ideal candidates for molecular wires, they show impressive nonlinear optical (NLO) properties, and they are invaluable building blocks to carbon-rich architectures. Conversely, the potential of cumulenes to function as conjugated materials remains essentially unexplored, due the limited number of known derivatives. The synthesis and chemistry of polyynes and cumulenes currently relies on a rather small toolbox of reactions and few have proven to be broadly applicable to extended polyynes and cumulenes. Beyond synthetic difficulties, however, lie significant challenges due to the instability/reactivity of polyynes and cumulenes, and this translates directly to the fact that very little has been accomplished toward the use of these unique molecules in real world devices. The research outlined in this proposal aims to solve the problem of polyyne and cumulene stability, through development of synthetic methods to form derivatives stabilized through mechanical bonds, i.e., rotaxanes. The thus formed rotaxanes will provide products for fundamental investigations, as well as for incorporation into nanoscale devices. The workplan consists of three areas of discovery. First, Work-Package 1 will optimize the synthetic methods for polyyne rotaxane, including substrates, reaction conditions, transition metal catalyst, solvent, and the size and functionality of the macrocyclic component. Next we strive to evaluate and refine parameters to form stabilized polyynes, in comparison to their naked, non-rotaxane analogs. The successful conclusion of this last point would offer polyynes of unprecedented length, to study the properties of carbyne. Work-Package 2 then explores stoppers that might be appended to the termini of the polyyne. The main goals here center on the formation of functionalized polyyne rotaxanes. Targeted groups include aromatic and heteroaromatic moieties that provide molecular wires for attachment to metal or graphene electrodes. Alternatively, donor and acceptor (D-A) groups will be attached to offer polarized, push-pull polyynes. D-A polyynes will be studied in comparison to known D-A polyenes, to determine the efficiency of triple bonds to mediate communication, as well as the formation of optimized NLO materials. Finally, protocols developed for polyyne rotaxanes will be adapted to form cumulene rotaxanes (Work-Package 3). To date, derivatives longer than [7]cumulenes are insufficiently stable for extensive studies in solution or the solid state. As a result, the compounds provided by the proposed research will give the first opportunity to probe the properties of longer members of this class of sp-carbon oligomers.