Light-Controlled Conductance Using Molecular Switches

A great challenge to present-day applied science is to develop electronic devices at the nanometer scale based on molecules. Diarylethenes are promising synthetic photoswitchable (photochromic) molecules because of the outstanding fatigue-resistant light-induced reversible transformation as they undergo interconversion between two isomers, each having different charge transport properties. Progress towards the development of light switchable electronic devices based on diarylethene photochromic molecular switches is described in this thesis. The main focus is on fundamental aspects that require resolution before a fully operational device can be constructed. The central questions of the research are: synthetic availability and cost of the molecules of interest, fundamental aspects of photochemical switching (reversibility, fatigue efficiency), influence of surface anchoring on the reversibility of the switching processes, effects of different surfaces on the organization of molecules, charge transport properties, scaling down to the nanoscale, i.e. to the single molecule level and finally, can conductivity switching be realized with a single molecule? Five experimental chapters summarize important findings such as: a dramatic conductance enhancement of more than two orders of magnitude upon optical switching between two isomers of a diarylethene molecule sandwiched between metallic electrodes, a quenching of photoreactions induced by the presence of metallic surfaces resulting in an irreversible switching behavior, a strong temperature dependence of the ring opening process and a new effect of substrate mediated intermolecular interactions on the self-assembly of molecules on surfaces. Finally, a reversible light-induced switching of conductance is demonstrated for individual molecules.