Molecular switches for nano-scale devices

Molecular machines based on interlocked molecules such as rotaxanes and catenanes are outlined in chapter 1. They display controllable mechanical motions driven by external stimuli. The intrinsric switching property of the molecules has become the basis for the fabrication of molecular switch tunnel junction (MSTJ) devices. A two-dimensional crossbar circuit that relies on redox-switchable molecules to demonstrate a 64-bit molecular memory chip adds to the promising future of molecular electronics.; Redox-switchable [2]rotaxanes as key molecular components for the fabrication of molecular-based devices are described in chapter 2. Their dumbbell components contain (i) one tetrathiafulvalene (TTF) unit and (ii) either one or two 1,5-dioxy-naphthalene (DNP) ring systems as recognition sites for a cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component. All of the rotaxanes exist almost exclusively as a single translational isomer and show excellent reversible switching behavior upon oxidation/reduction. These redox-switchable rotaxanes display almost 100% switching efficiency.; Shuttling rates of the CBPQT4+ ring between the TTF unit and DNP ring system in solution are reported in chapter 3. Two sets of three different degenerate [2]rotaxanes were made with varying spacer units. One set incorporated two TTF recognition sites, and the other one incorporated two DNP ring systems. A relatively small difference in the barriers for the shuttling process in the [2]rotaxanes containing the different spacers was observed, in contrast to a large difference between the TTF-containing rotaxanes (18 kcal mol-1) and the DNP-containing rotaxanes (15 kcal mol-1). This data provides further evidence that the mechanism for the operation of rotaxane-based molecular devices involves mechanical ring movement.; Chapter 4 describes an in situ Fourier-transform infrared (FTIR) spectroscopic technique that has been developed to monitor molecular behavior in single-molecule thick nanoelectronic devices. This technique is applicable to a range of molecular-based devices and has the potential to provide researchers in the field with a tool to understand the molecular behavior that contributes to device performance.