Moore's law is an established empirical law of both technology and economics. It demonstrates that computational power available to a system has grown exponentially since ca. 1965, due to decreasing character size of the components on integrated circuits. This trend is presently being maintained by well established top-down techniques such as photolithography, but these techniques are reaching their fundamental size limits. One of the most promising approaches for the continuation of Moore's law is the development of molecular electronics. A molecular rectifier is a nanoscale molecular system which conducts electrical current better in one direction than the other; it is the molecu]ar
equivalent to the inorganic, solid-state p-n junction.
There are three main challenges facing molecular rectifiers if they are ever to be realized as realistic challengers to conventional electronic components. These challenges are associated with: the efficiency of the rectification process, the amount of electrons
transmitted in one direction relative to the other; the ability to control the direction of the rectification; and finally, the ability to integrate the molecular electronic components into real systems.
In this thesis, significant advancements in answering two of these challenges are presented. Firstly a novel technique of constructing rectifying molecular junctions comprised of discrete, ionically coupled, layers of a cationic acceptor ( 4,4'-bipyridinium)
and an anionic donor (copper phthalocyanine-3,4',4",4"'-tetrasulfonate) are reported. This is the first example of a fabrication technique that has subsequently been employed,
to achieve the highest, confirmed levels of rectification for a molecular system. Secondly two techniques are reported for reversing the direction of rectification in a molecular system. In both cases this reversal is achieved by the switching of the internal molecular dipole, firstly by the switching of the orientation of two isomers and secondly by the controlled placement of counterions along the rectifying chromophore.