Polyyne and cumulene rotaxanes: Toward insulated molecular wires

由sp-杂化碳构建的低聚物分子，即多炔和累积多烯，由于其独特的一维骨架而非常重要。它们也是预测碳炔同素异形体性质的关键环节。在应用层面上，多炔是分子导线的理想候选者，它们显示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构建块。相反，由于已知衍生物的数量有限，累积多烯作为共轭材料的潜力基本上仍未被探索。多炔和累积多烯的合成和化学目前依赖于一个相当小的反应工具箱，很少有被证明是广泛适用于扩展的多炔和累积多烯。然而，除了合成困难之外，由于多炔和累积多烯的不稳定性/反应性而存在重大挑战，并且这直接转化为在真实的世界装置中使用这些独特分子的成就非常少的事实。该提案中概述的研究旨在通过开发合成方法以形成通过机械键稳定的衍生物，即，轮烷。由此形成的轮烷将为基础研究提供产品，以及纳入纳米级器件。工作计划包括三个发现领域。首先，工作包1将优化聚炔轮烷的合成方法，包括底物、反应条件、过渡金属催化剂、溶剂以及大环组分的大小和官能度。接下来，我们努力评估和完善参数，以形成稳定的多炔，与他们的裸露，非轮烷类似物。这最后一点的成功结论将提供前所未有的长度的多炔，以研究碳炔的性质。然后，工作包2探讨了可能附加到聚炔末端的塞子。这里的主要目标集中在形成官能化的聚炔轮烷。靶向基团包括提供用于连接到金属或石墨烯电极的分子线的芳族和杂芳族部分。或者，供体和受体（D-A）基团将被连接以提供极化的推拉多炔。D-A多炔将与已知的D-A多烯进行比较研究，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，为聚炔轮烷开发的方案将被修改以形成累积多烯轮烷（工作包3）。迄今为止，长于[7]累积多烯的衍生物在溶液或固态中的广泛研究中不够稳定。因此，拟议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.