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According to the famous axiom known as Moore’s Law the number of transistors that can be etched on a given piece of ultra-pure silicon, and therefore the computing power, will double every 18 to 24 months. However, around 2020 hardware manufacturers will have reached the physical limits of silicon. A proposed solution to this dilemma is molecular electronics. Within this field researchers are attempting to develop individual organic molecules and metal complexes that can act as molecular equivalents of electronic components such as wires, diodes, transistors and capacitors.

In this work we have synthesized a number of new bi- and terdentate thiophenyl pyridine and pyridyl thienopyridine ligands and compared the electrochemical, structural and photophysical properties of their corresponding Ru(II) complexes with Ru(II) complexes of a variety of ligands based on 6-thiophen-2-yl-2,2'-bipyridine and 4-thiophen-2-yl-2,2'-bipyridine motifs. While the electrochemistry of the Ru(II) complexes were similar to that of unsubstituted [Ru(bpy)₃]²⁺ and [Ru(tpy)₂]²⁺, substantial differences in luminescence lifetimes were found. Our findings show that, due to steric interactions with the auxiliary bipyridyl ligands, luminescence is quenched in Ru(II) complexes that incorporate the 6-thiophen-2-yl-2,2'-bipyridine motif, while it was comparable with the luminescence of [Ru(bpy)₃]²⁺ in the Ru(II) complexes of bidentate pyridyl thienopyridine ligands. The luminescence of the Ru(II) complexes based on the 4-thiophen-2-yl-2,2'-bipyridine motif was enhanced compared to [Ru(bpy)₃]²⁺ which indicates that complexes of this category may be applicable for energy/electron-transfer systems.

At the core of molecular electronics is the search for molecular ON/OFF switches. Based on the ability of the ligand 6-thiophen-2-yl-2,2'-bipyridine to switch reversibly between cyclometallated and non-cyclometallated modes when complexed with Ru(tpy) we have synthesized a number of complexes, among them a bis-cyclometallated switch based on the ligand 3,8-bis-(6-thiophen-2-yl-pyridin-2-yl)-[4,7]phenanthroline, and examined their electrochemical properties. Only very weak electronic coupling could be detected, suggesting only little, if any, interaction between the ruthenium cores.

The earliest landmark in computer technology was construction of the Electronic Numerial Integrator and Computer, ENIAC. Computational switching was performed with vacuum tubes and relays, rather large in size, making this computer rather unwieldy. The next milestone came with the integration of transistors into computers as the switching component. Since then, transistors have been miniaturised dramatically, resulting in the amount of components integrated on a computer chip increasing logarithmically with time. The components are nowadays so small and so densely packed that problems with leak currents and cross-talk can arise and the lower limit for transistor size will soon be reached. In order to meet increasing demands on the size and performance of electronics, a new paradigm is due – the molecular electronics approach.

Oligothiophenes have been shown to possess the physical and chemical characteristics required for electron/energy transport in molecular systems. However oligothiophenes must be electronically coupled to other components within a molecular circuit for them to be functional. In this work, different modes of incorporation of [2,2’]-bipyridinyl functionalities onto the ends of prototypic oligothiophene wires have been examined. The bipyridine connectors allow complexation to metal centres which can then function as a source or sink of electrons in the circuit. Ruthenium tris-bipyridine complexes, in particular, possess interesting electrochemical and photophysical characteristics, making them suitable for use in molecular electronics.

This thesis reports synthetic strategies to a range of novel ligands based on the [2,2’]-bipyridinyl system, together with a study of the redox and fluorescence properties of their ruthenium tris-bipyridine complexes. The mode of connection between the chelating bipyridine and the first member of the oligothiophene chain was found to have a profound effect upon the fluorescence lifetimes and intensities of the resulting complexes. The discovery of complexes exhibiting long and intense fluorescence (a requirement for directed electron/energy transfer within molecular networks) thus forms an important design element in future prototypes.