Molecular tectonics: Supramolecular two-dimensional nanopatterning of surfaces by self-assembly.

摘要

In recent years, molecular tectonics has been employed as an efficient strategy in the construction of supramolecular architectures in three dimensions (3D). The building blocks used in this strategy, which have been called tectons, have structures with well-defined geometries and multiple functional groups that control intermolecular association by forming directional interactions, such as hydrogen bonds. A new opportunity exists to adopt this strategy to create well-defined 2D molecular networks on the surfaces of various substrates, such as graphite. In this dissertation, a series of new tectons have been purposefully designed and synthesized for nanopatterning surfaces, and their adsorption on highly oriented pyrolytic graphite (HOPG) has been thoroughly examined by scanning tunneling microscopy (STM).;Specifically, the tectons investigated herein incorporate systematic changes of molecular length, cores, functional groups, and molecular geometries. The basic cores, which are aromatic systems such as benzene, naphthalene, and anthracene, are grafted to conjugated linkers, including acetylene and arylacetylene, and to various functional groups with different abilities to engage in intermolecular interactions, including diaminotriazine groups, carboxylic acids, and related substituents. The observation of diverse nanopatterns has led to a deeper understanding of (1) how the basic backbone interacts with surfaces, (2) how the functional groups modify the behavior of the backbone, and (3) how the formation of interadsorbate interactions further influences adsorption.;Our work demonstrates that rational 2D and 3D molecular assembly can be achieved and analyzed by an integrated approach using the tools of STM, X-ray diffraction, computation, and molecular synthesis. Furthermore, our work confirms that molecules with well-defined shapes and multiple sites that engage in strong directional interactions are a consistently productive source of new materials with properties not previously observed.;Key words: Molecular tectonics, 2D nanopatterning, scanning tunneling microscopy (STM), self-assembly.;To understand the details of molecular adsorption, multiple methods of characterization and analysis have been used in this work, including (1) direct examination of adsorption by STM, (2) systematic alteration of the structure of the adsorbate to reveal how the self-assembled 2D nanopatterns changes, (3) comparison of the observed 2D nanopatterns with those seen in 3D structures by X-ray crystallography, and 4) theoretical calculations to help disclose the origin of molecular adsorption.