Control of 2-Dimensional Molecular Self-Organisation: Towards Designed Surfaces

在传感器、分子电子学、智能涂层、有机太阳能电池、催化剂、医疗设备等纳米技术中，表面有机分子单分子膜通常是核心工作部件。该领域的一个核心挑战是实现在表面可控地创建所需的2D分子结构。在这一背景下，过去十年见证了表面上2D分子组装的自下而上的自组织发生了真正而重大的变化。通过自组织形成的种类繁多和丰富的分子结构现在有力地推动了这种争论，它强烈支持“自下而上”的构建策略，这种策略利用了纳米这两个强大的属性--精确(自上而下的方法无法获得)和高度并行的制造(原子/分子操纵是不可能的)。因此，自下而上的表面分子组装具有成为21世纪纳米技术主导合成协议的真正可能性。通过扫描探针显微镜和先进的表面光谱成像，这些在2D表面的分子结构的范围和多样性已经在纳米尺度上被直接捕获。然而，目前，该领域主要局限于一种“制造和查看”的方法，对于最终控制分子表面组装的任何参数都知之甚少。例如：(1)分子在表面的组装表现出高度多态的行为，对组装的先验控制几乎不存在；(2)对驱动分子识别和组装的许多相互作用的影响和平衡知之甚少(分子-分子相互作用，包括分散、定向氢键和强烈的静电和共价相互作用)；(3)表面-分子相互作用的作用在很大程度上是未知的，尽管它们在分子的扩散和随后的组装中发挥着重要作用；(4)有充分的证据表明，自组装动力学是决定最终结构的主要因素，往往驱动多态行为并导致广泛不同的结果，具体取决于形成条件；(5)一系列额外的表面现象也影响组装，例如分子之间的化学反应、分子的热激活内部自由度、表面重构和通过配位表面原子进行的共同组装。该项目的主要目标是从实验现象报告发展到基于知识的设计，其中心目标是确定在给定的实验条件下，热力学、熵、动力学和化学因素在决定表面分子组织方面所起的作用。为了应对这一挑战，需要采取双管齐下的方法，在雄心勃勃和全面的理论开发的同时，将强大的成像和光谱工具应用于相同的系统。这种实验和理论的结合对于发展一种基本的理解是绝对必要的，这将使人们能够提出一种在表面上进行受控和工程自组装的路线图，最终将允许人们随意‘拨号’所需的结构。四类重要且性质不同的表面组装将被研究：分子自组装；分级自组装；金属-有机自组装；以及表面共价组装。

Organic molecular monolayers at surfaces often constitute the central working component in nanotechnologies such as sensors, molecular electronics, smart coatings, organic solar cells, catalysts, medical devices, etc. A central challenge in the field is to achieve controlled creation of desired 2D molecular architectures at surfaces. Within this context, the past decade has witnessed a real and significant step-change in the 'bottom-up' self-organisation of 2D molecular assemblies at surfaces. The enormous variety and abundance of molecular structures formed via self-oeganisation has now critically tipped the argument strongly in favour of a 'bottom-up' construction strategy, which harnesses two powerful attributes of nanometer-precision (inaccessible to top-down methods) and highly parallel fabrication (impossible with atomic/molecular manipulation). Thus, bottom-up molecular assembly at surfaces holds the real possibility of becoming a dominating synthesis protocol in 21st century nanotechnologies Uniquely, the scope and versatility of these molecular architectures at 2D surfaces have been directly captured at the nanoscale via imaging with scanning probe microscopies and advanced surface spectroscopies. At present, however, the field is largely restricted to a 'make and see' approach and there is scarce understanding of any of the parameters that ultimately control molecular surface assembly. For example: (1) molecular assemblies at surfaces show highly polymorphic behaviour, and a priori control of assembly is practically non-existent; (2) little is understood of the influence and balance of the many interactions that drive molecular recognition and assembly (molecule-molecule interactions including dispersion, directional H-bonding and strong electrostatic and covalent interactions); (3) the role of surface-molecule interactions is largely uncharted even though they play a significant role in the diffusion of molecules and their subsequent assembly; (4), there is ample evidence that the kinetics of self-assembly is the major factor in determining the final structure, often driving polymorphic behaviour and leading to widely varied outcomes, depending on the conditions of formation; (5) a gamut of additional surface phenomena also also influence assembly e.g. chemical reactions between molecules, thermally activated internal degrees of freedom of molecules, surface reconstructions and co-assembly via coordinating surface atoms. The main objective of this project is to advance from experimental phenomena-reporting to knowledge-based design, and its central goal is to identify the role played by thermodynamic, entropic, kinetic and chemical factors in dictating molecular organisation at surfaces under given experimental conditions. To address this challenge requires a two-pronged approach in which ambitious and comprehensive theory development is undertaken alongside powerful imaging and spectroscopic tools applied to the same systems. This synergy of experiment and theory is absolutely essential to develop a fundamental understanding, which would enable a roadmap for controlled and engineered self-assembly at surfaces to be proposed that would, ultimately, allow one to 'dial up' a required structure at will. Four important and qualitatively different classes of assembly at surfaces will be studied: Molecular Self-Assembly; Hierarchical Self-Assembly; Metal-Organic Self Assembly; and, on-surface Covalent Assembly.