Two-Dimensional Assembly of Functional Organic Molecular Networks

二维纳米材料，如石墨烯及其复合材料，在先进的电子、能源、分离甚至润滑材料应用方面具有巨大的潜力。然而，这些碳纳米材料相对简单的化学组成的微小共价变化会对其性能产生相当大的影响，从而使其难以合理地设计用于目标应用。来自超分子自组装过程的材料有可能克服这一缺点，因为它利用了设计更简单的分子成分，这些分子成分可以通过有利的非共价分子间相互作用（如氢和卤素键）将自己组织成复杂的纳米结构。作为一个自发的平衡过程，分子组分的自组装通过初始成核事件进行，随后生长形成有序的纳米结构，代表系统的最小自由能状态。通过在表面上执行这些热力学控制过程，我们可以获得定义良好的二维纳米级结构，其形态（例如，表面模式和结构），密度和/或孔隙度以及其组成分子的精确配置和非共价相互作用产生的固有功能特性。高度定向氢键相互作用的自互补氢键基序（唑、内酰胺-乳酰胺、酰胺）单元将被用于将氧化还原活性分子构建块组装成导电表面（例如Cu、Au和/或石墨烯）上的纳米级薄二维网络。这些分子中存在的氢键位点的大小、形状和数量将被系统地修改，以便更好地理解它们的结构设计如何影响所得到的二维材料的包装形态、密度和孔隙度。表面和探针二维网络结构的基本自组装机制将使用各种先进的光谱学（x射线光电子能谱），粉末x射线衍射，宽和小角度x射线衍射，高分辨率扫描隧道和电子显微镜进行评估。固态伏安法、电化学阻抗和电导率测量将在单晶和制备的微晶薄膜上进行，以评估密集排列的氢键在空间中传递电子的有效性，即横向跨越自组装层，以提供高导电性。最后，通过与工程团队的合作，我们还将研究这些自组装氢键表面的纳米摩擦学特性，这有望为水化润滑机制产生低摩擦提供新的范例。在此项目期间开展的工作将有助于快速发展的低/二维材料领域的研究工作，其中包括金属配位聚合物，共价有机框架（COFs）和超分子聚合物的进展，并将与EPSRC优先（增长）领域的利益高度相关：储能，能源应用材料，以及维护领域：凝聚态物质（电子结构）、电化学科学、石墨烯与碳纳米技术、表面科学、合成超分子化学。

Two-dimensional nanomaterials-such as graphene and its composites-hold enormous potential for use in advanced electronics, energy, separation, and even lubrication materials applications. However, small covalent changes to the relatively simple chemical composition of these carbon nanomaterials can cause rather large effects on their properties, thus making it difficult to rationally design them for target applications. Materials derived from supramolecular self-assembly processes have the potential to overcome the drawback by taking advantage of simpler-to-design molecular components that can organise themselves into complex nanostructures via favourable non-covalent intermolecular interactions such as hydrogen and halogen bonding. As a spontaneous equilibrium process, self-assembly of the molecular components proceeds via an initial nucleation event that is followed by growth to form an ordered nanostructure that represents minimum free-energy state of the system. By carrying out these thermodynamically-controlled processes on a surface, we can gain access to well-defined two-dimensional, nanometres-thick architectures whose morphology (e.g., surface pattern and architecture), density and/or porosity, and inherent functional properties arise from the precise configuration and non-covalent interactions of its constituent molecules.Highly directional hydrogen bonding interactions of self-complementary hydrogen bond motifs (azoles, lactam-lactim, amide) units will be exploited to assemble redox-active molecular building blocks into nanoscopically thin two-dimensional networks on conductive surfaces (e.g., Cu, Au and/or graphene). The size, shape and number of hydrogen bonding sites present in these molecules will be modified systematically in order to gain a better understanding of how their structural design affects the packing morphology, density and porosity of the resulting two-dimensional material. Fundamental self-assembly mechanisms on surfaces and probe two-dimensional network structures will be assessed using a variety of advanced spectroscopies (X-ray photoelectron spectroscopy), powder X-ray diffraction, wide and small-angle X-ray diffraction, and high resolution scanning tunneling and electron microscopies. Solid-state voltammetry, electrochemical impedance and conductivity measurements will be carried out on single crystals and as-prepared microcrystalline thin films to assess the effectiveness of densely-packed hydrogen bonds to transfer electrons through space, i.e., laterally across the self-assembled layers, to afford high conductivity. Finally, through collaborations with Engineering groups, we will also investigate the nanotribological properties of these self-assembled hydrogen bonded surfaces, which are anticipated to provide a new paradigm for generating low friction as a result of hydration lubrication mechanisms. The work carried out during this project will contribute to research efforts in the rapidly growing field of low-/two-dimensional materials, which has included advances in metal coordination polymers, covalent organic frameworks (COFs) and supramolecular polymers, and will be highly relevant to the interests of EPSRC Priority (Grow) Areas: Energy storage, Materials for energy applications, as well as Maintain Areas: Condensed matter (electronic structure), Electrochemical sciences, Graphene and carbon nanotechnology, Surface science, Synthetic supramolecular chemistry.