Octyl-decorated Fréchet-type dendrons : a general motif for visualisation of static and dynamic behaviour using scanning tunnelling microscopy

摘要

Firstly, a short overview on supramolecular chemistry including definitions, basic principles and examples taken from the literature of 2D and 3D self-assembly processes is given in Chapter 1. The introduction is completed by some general ideas of dendrimer chemistry. In the second Chapter the techniques used in this thesis are introduced with a special focus on scanning tunnelling microscopy (STM). Besides the mode of operation and the data processing, the historical background is briefly described. The following four Chapters present STM studies of monolayers formed by different types of compounds, all functionalised with Fréchet-type dendrons. Not only static features of monolayers such as conformational analysis of single molecules have been investigated, but also dynamic processes such as delayed conversion of a whole domain and conformational changes by protonation have been examined. The 2D properties of monolayers on a graphite surface have been compared with the X-ray data of 3D single crystals. For two compounds, the same molecular arrangement has been detected in monolayers on graphite and in single crystals. Together with organic molecules, the self-assembly of metal complexes possessing tpy ligands and organometallic species with platinum(II) bis(alkynyl) units has been examined. Not all of these metal complexes were stable under the scanning conditions used in STM. A synthetic programme leading to dendrimer-functionalised organic and organometallic compounds has been developed. Discussions of synthetic routes are given at the beginning of each Chapter. Chaptercompares X-ray diffraction methods with STM, the two main analysis tools used for investigation of self-organised assemblies in the solid state in this thesis. In the second part of Chapter 7, the results presented in the previous Chapters are discussed with some general reflections on the self-assembling properties of Fréchet-type dendrimers with pendant octyl groups. Additional to the studies of self-assembled monolayers, the formation of metallomacrocycles has been investigated using two novel homoditopic tpy ligands. This work is presented in Chapter 8. It was demonstrated that the ring-size depends on the metal used for the cyclisation. Furthermore, some of the macrocycles formed self-assembled monolayers on graphite, which have been examined using STM. One homoditopic ligand formed a molecular square by complexation with an iron(II) salt which was analysed using single crystal X-ray diffraction. This thesis has brought together the realms of chemical design with studies of the physical behaviour of the envisioned molecules on the surface. It has been demonstrated that Fréchet-type dendrimers with octyl end-groups are a general motif for visualisation of static and dynamic behaviour using STM.