| Crystal engineering deals with the design of ordered arrays of molecular building blocks and is of high importance in nanotechnology, electronics and in the pharmaceutical industry. While organic synthesis provides access to a wide range of molecules, control over their intermolecular interactions is the major challenge taken on by crystal engineering. This thesis focuses on the surface self-assembly of carboxylic acids, as a convenient model system to study general factors governing self-assembly. It is a step towards the rational design of materials with desired compositions, morphologies and functionalities.;To elucidate the effect of building block structure on self-assembly, architectures formed by cyclic homo-dimers of carboxylic groups (i.e. structures containing the R22(8) synthon) are analyzed. Results are given in the form of case-studies covering formation of H-bonded macrocycles, chains, ladders, rotaxanes, catenanes and various 2D and 3D nets. Similar analyses of other H-bonding carboxylic acid assemblies are used to highlight the most important aspects of the carboxylic group's supramolecular reactivity, as well as the applications thereof.;A detailed study of the surface co-assembly of trimesic acid (TMA) with n-alcohols is presented. Investigating this single system allows for the observation of a wide variety of phenomena that were previously only studied separately, and on structurally different systems. This enables relevant comparisons between molecular structure and the many factors governing self-assembly at the liquid-solid interface. The periodicity and fine structure of the TMA-alcohol SAMN is conveniently modulated by varying n-alcohol length and parity, representing an important step towards rational molecular nanopatterning of surfaces using the principles of crystal engineering.;Relationships between building block structures and the stability of resulting carboxylic homosynthons (viz. the cyclic dimer R22(8), the trimer R33(12) and the hexamer R66(24)) are established through a combination of empirical observations and quantum-chemical calculations. Thus, formation of specific homosynthons is found to depend strongly upon steric intermolecular interactions, as well as upon the relative packing efficiencies of competing polymorphs. These findings allow explanation of the structure and chiral nature of the self-assembly formed by terthienobenzenetricarboxylic acid (TTBTA). Additionally, the rational design of supramolecular networks formed by the R66(24) homosynthon is demonstrated for the first time, using triethynylbenzenetricarboxylic acid (TEBTA).;Specifically, this thesis presents a systematic investigation of hydrogen-bonded (H-bonded) assemblies of carboxylic building blocks on surfaces (i.e. 2D crystals), complemented by studies of their assemblies in bulk solid state (i.e. 3D crystals). This work provides new insights into the complex relationship between building block structures, H-bonding synthons and self-assembly outcomes using scanning tunneling microscopy (STM), X-ray diffraction crystallography and quantum-mechanical calculations. Consideration of these insights has resulted in the supramolecular design of novel self-assembled molecular networks (SAMNs), described below.;Finally, porous TMA networks are used as host matrices to control and study the self-assembly of new pi-functional guest molecules. Specifically, two semiconducting heterocirculenes (sulflower and selenosulflower) are imaged by STM with sub-molecular resolution, enabling the study of adsorption-desorption dynamics, host-guest interactions, and stable pi-pi stacking architectures. The latter findings open up the possibility to form multilayers of host-guest architectures with high potential for applications in optoelectronic devices. |
