Mechanophores can be used to produce strain-dependent covalent chemical responses in polymeric materials, including stress strengthening, stress sensing and network remodelling. In general, it is desirable for mechanophores to be inert in the absence of force but highly reactive under applied tension. Metallocenes possess potentially useful combinations of force-free stability and force-coupled reactivity, but the mechanistic basis of this reactivity remains largely unexplored. Here, we have used single-molecule force spectroscopy to show that the mechanical reactivities of a series of ferrocenophanes are not correlated with ring strain in the reactants, but with the extent of rotational alignment of their two cyclopentadienyl ligands. Distal attachments can be used to restrict the mechanism of ferrocene dissociation to proceed through ligand ‘peeling’, as opposed to the more conventional ’shearing’ mechanism of the parent ferrocene, leading the dissociation rate constant to increase by several orders of magnitude at forces of ~1 nN. It also leads to improved macroscopic, multi-responsive behaviour, including mechanochromism and force-induced cross-linking in ferrocenophane-containing polymers.

机械载体可用于在聚合物材料中产生应变依赖性共价化学反应，包括应力强化、应力传感和网络重塑。通常，希望机械载体在没有力的情况下是惰性的，但在施加的张力下具有高反应性。茂金属具有无力稳定性和力耦合反应性的潜在有用组合，但这种反应性的机理基础在很大程度上仍未探索。在这里，我们使用单分子力谱表明一系列二茂铁的机械反应性与反应物中的环应变无关，但与它们的两个环戊二烯基配体的旋转排列程度有关。远端附件可用于限制二茂铁解离机制通过配体“剥离”进行，这与母体二茂铁更传统的“剪切”机制相反，导致解离速率常数在力下增加几个数量级~1 nN。它还导致改进的宏观、多响应行为，包括机械变色和含二茂铁聚合物中的力诱导交联。