Photoswitching behavior of individual organic molecules was imaged by annular dark-field scanning transmission electron microscopy (ADF-STEM) using a highly electron beam transparent graphene support. Photoswitching azobenzene derivatives with ligands at each end containing single transition-metal atoms (Pt) were designed (Pt-complex), and the distance between the strong ADF-STEM contrast from the two Pt atoms in each Pt-complex is used to track molecular length changes. UV irradiation was used to induce photoswitching of the Pt complex on graphene, and we show that the measured Pt–Pt distances within isolated molecules decrease from ∼2.1 nm to ∼1.4 nm, indicative of a trans-to-cis isomerization. Light illumination of the Pt-complex on the graphene support also caused their diffusion out from initial clusters to the surrounding area of graphene, indicating that the light-activated mobilization overcomes the intermolecular van der Waals interactions. This approach shows how individual isolated heavy metal atoms can be included as markers into complex molecules to track their structural changes using ADF-STEM on graphene supports, providing an effective method to study a diverse range of complex organic materials at the single molecule level.

中文翻译：

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使用单个金属原子标记的光开关分子构象的直接成像

通过使用高电子束透明石墨烯载体的环形暗场扫描透射电子显微镜（ADF-STEM）对单个有机分子的光开关行为进行成像。设计了在每个末端都带有一个过渡金属原子（Pt）的配体的光开关偶氮苯衍生物（Pt-络合物），并使用了ADF-STEM与每个Pt络合物中两个Pt原子之间的强对比形成的距离来跟踪分子长度变化。UV照射用于诱导在Pt上的石墨烯复合物的光控，和我们表明，分离的分子内所测量的Pt-铂距离从减少~2.1纳米至〜1.4纳米，表示的反式-到-顺异构化。石墨烯载体上Pt配合物的光照也导致它们从初始簇扩散到石墨烯的周围区域，表明光活化的动员克服了分子间范德华相互作用。该方法显示了如何使用石墨烯载体上的ADF-STEM将单个孤立的重金属原子作为标记物包含在复杂分子中，以跟踪其结构变化，从而提供了一种有效的方法来研究单分子水平上各种复杂的有机材料。