Chemistry Research Laboratory, Department of Chemistry, University of Oxford , Mansfield Road, Oxford OX1 3TA, United Kingdom.
Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom.
J Am Chem Soc. 2018 Feb 7;140(5):1924-1936. doi: 10.1021/jacs.7b12819. Epub 2018 Jan 30.
By addressing the challenge of controlling molecular motion, mechanically interlocked molecular machines are primed for a variety of applications in the field of nanotechnology. Specifically, the designed manipulation of communication pathways between electron donor and acceptor moieties that are strategically integrated into dynamic photoactive rotaxanes and catenanes may lead to efficient artificial photosynthetic devices. In this pursuit, a novel [3]rotaxane molecular shuttle consisting of a four-station bis-naphthalene diimide (NDI) and central C fullerene bis-triazolium axle component and two mechanically bonded ferrocenyl-functionalized isophthalamide anion binding site-containing macrocycles is constructed using an anion template synthetic methodology. Dynamic coconformational anion recognition-mediated shuttling, which alters the relative positions of the electron donor and acceptor motifs of the [3]rotaxane's macrocycle and axle components, is demonstrated initially by H NMR spectroscopy. Detailed steady-state and time-resolved UV-vis-IR absorption and emission spectroscopies as well as electrochemical studies are employed to further probe the anion-dependent positional macrocycle-axle station state of the molecular shuttle, revealing a striking on/off switchable emission response induced by anion binding. Specifically, the [3]rotaxane chloride coconformation, where the ferrocenyl-functionalized macrocycles reside at the center of the axle component, precludes electron transfer to NDI, resulting in the switching-on of emission from the NDI fluorophore and concomitant formation of a C fullerene-based charge-separated state. By stark contrast, in the absence of chloride as the hexafluorophosphate salt, the ferrocenyl-functionalized macrocycles shuttle to the peripheral NDI axle stations, quenching the NDI emission via formation of a NDI-containing charge-separated state. Such anion-mediated control of the photophysical behavior of a rotaxane through molecular motion is unprecedented.
通过控制分子运动的挑战，机械互锁分子机器在纳米技术领域的各种应用中具有很大的潜力。具体来说，通过设计操纵电子给体和受体部分之间的通讯途径，这些部分被战略性地集成到动态光活性轮烷和索烃中，可能会导致高效的人工光合作用器件。在这一追求中，使用阴离子模板合成方法构建了一种由四个站双萘二酰亚胺（NDI）和中央 C 富勒烯双三唑鎓轴组件以及两个机械键合的二茂铁基功能化异苯并酰胺阴离子结合位点的大环组成的新型[3]轮烷分子梭。最初通过 H NMR 光谱证明了动态共构阴离子识别介导的穿梭，这改变了[3]轮烷大环和轴组件的电子给体和受体图案的相对位置。详细的稳态和时间分辨的紫外可见红外吸收和发射光谱以及电化学研究进一步探测了分子梭的阴离子依赖性位置大环-轴站状态，揭示了阴离子结合诱导的惊人的开/关可切换发射响应。具体而言，[3]轮烷氯化物共构形式中，二茂铁基大环位于轴组件的中心，阻止电子转移到 NDI，导致 NDI 荧光团的发射开启，并形成基于 C 富勒烯的电荷分离态。相比之下，在不存在作为六氟磷酸盐盐的氯化物的情况下，二茂铁基大环梭至外围 NDI 轴站，通过形成包含 NDI 的电荷分离态来猝灭 NDI 发射。这种通过分子运动对轮烷光物理行为的阴离子介导控制是前所未有的。
