The Bernal Institute and Department of Chemical Sciences, School of Natural Sciences, University of Limerick (UL), Limerick V94 T9PX, Ireland.
The Bernal Institute and Department of Physics, School of Natural Sciences, University of Limerick (UL), Limerick V94 T9PX, Ireland.
J Am Chem Soc. 2021 Jun 23;143(24):9060-9069. doi: 10.1021/jacs.1c02481. Epub 2021 Jun 11.
Nanostructures that are inaccessible through spontaneous thermodynamic processes may be formed by supramolecular self-assembly under kinetic control. In the past decade, the dynamics of pathway complexity in self-assembly have been elucidated through kinetic models based on aggregate growth by sequential monomer association and dissociation. Immiscible liquid-liquid interfaces are an attractive platform to develop well-ordered self-assembled nanostructures, unattainable in bulk solution, due to the templating interaction of the interface with adsorbed molecules. Here, we report time-resolved UV-vis spectroscopic observations of the self-assembly of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrin (ZnTPPc) at an immiscible aqueous-organic interface. We show that the kinetically favored metastable J-type nanostructures form quickly, but then transform into stable thermodynamically favored H-type nanostructures. Numerical modeling revealed two parallel and competing cooperative pathways leading to the different porphyrin nanostructures. These insights demonstrate that pathway complexity is not unique to self-assembly processes in bulk solution and is equally valid for interfacial self-assembly. Subsequently, the interfacial electrostatic environment was tuned using a kosmotropic anion (citrate) in order to influence the pathway selection. At high concentrations, interfacial nanostructure formation was forced completely down the kinetically favored pathway, and only J-type nanostructures were obtained. Furthermore, we found by atomic force microscopy and scanning electron microscopy that the J- and H-type nanostructures obtained at low and high citric acid concentrations, respectively, are morphologically distinct, which illustrates the pathway-dependent material properties.
在动力学控制下，通过超分子自组装可以形成通过自发热力学过程无法获得的纳米结构。在过去的十年中，通过基于通过顺序单体缔合和解离进行聚集生长的聚合模型，阐明了自组装过程中途径复杂性的动力学。不混溶的液 - 液界面是开发有序自组装纳米结构的有吸引力的平台，由于界面与吸附分子的模板相互作用，在本体溶液中无法获得这些结构。在这里，我们报告了在不混溶的水 - 有机界面处锌（II）meso-四（4-羧基苯基）卟啉（ZnTPPc）自组装的时间分辨紫外 - 可见光谱观察。我们表明，动力学上有利的亚稳 J 型纳米结构快速形成，但随后转化为稳定的热力学有利的 H 型纳米结构。数值模拟揭示了两种平行且竞争的协同途径导致不同的卟啉纳米结构。这些见解表明，途径复杂性不仅对本体溶液中的自组装过程是独特的，而且对界面自组装同样有效。随后，使用亲水性阴离子（柠檬酸盐）来调整界面静电环境，以影响途径选择。在高浓度下，界面纳米结构的形成完全被强制沿动力学有利的途径进行，仅获得 J 型纳米结构。此外，我们通过原子力显微镜和扫描电子显微镜发现，在低柠檬酸浓度下获得的 J 型和 H 型纳米结构，分别在形态上是不同的，这说明了依赖途径的材料性质。
