Synthesis, characterisation and single molecule conductance measurements of organic molecules

The use of single molecules to construct electronic devices is an exciting prospect, and one that has long provided a driving force for research in the area of molecular scale electronics. In order for this emerging field to advance a deep understanding of the fundamental mechanisms that govern electron conduction at the molecular level is imperative. Recent developments in areas such as scanning tunnelling microscopy, have facilitated the determination of the electrical properties of single molecules tethered between two metallic contacts. The analysis and potentially tailoring of structure-property relationships is hugely important and could lead to new and unforeseen applications for this emerging field. The work presented herein details two major studies. The first is an investigation of the transport properties of a series of analogous molecules, which consist of a single benzene ring sandwiched between two alkyl chains of varying length. Prior to the work in this thesis one such molecule, and various substituted analogues thereof, had shown behaviour similar to what would be expected of a molecular equivalent of a double tunnelling barrier. The data presented here demonstrates a remarkably low dependence of this system on molecular length; this result contradicts the behaviour expected of a coherent transport mechanism. Moreover, the study of the orbital energies and densities of these molecules provides further evidence of a mechanism of conduction that is very different to that previously suggested for this system. The second study centres around the investigation of the conductance behaviour of 4,4’-bipyridine and some substituted analogues thereof; this study is presented in two parts. The first details attempts to synthesise planar analogues of 4,4’-bipyridine, as well the synthesis and reactivity of novel substituted bipyridines. The second part reports conductance data, electrochemical studies and theoretical calculations of properties of these molecules. The data presented provides new information regarding the relationship between electronic structure and conductance behaviour in this type of system.