Copyright WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2002. Supporting Information for ChemPhysChem Z401 Two-Dimensional Molecular Electronics Circuits Yi Luo, C. Patrick Collier, Jan O. Jeppesen, Kent A. Nielsen, Erica DeIonno, Greg Ho, Julie Perkins, Hsian-Rong Tseng, Tohru Yamamoto, J. Fraser Stoddart*, and James R. Heath* Introduction. In this supplement, we provide additional information related to the various control molecules and experiments utilized to establish the molecular structure / device property relationships that led to the mechanistic arguments in the paper. We also provide a more detailed description of the various measurement procedures, as well as the fabrication techniques for both the micrometer-scale and nanometer-scale devices utilized here. Finally, we provide synthetic details for some of the mechanically interlocked compounds and their precursors that were utilized here and whose synthesis has not been described previously in the literature. Control Devices for the [2]Rotaxane Molecular Switch Tunnel Junction Device. Several control compounds, in addition to the principal [2]rotaxanes ( I and II ) discussed in the text, were used [1,2] in this work They are illustrated in Figure A1. The [2]catenane and the [2]pseudorotaxane, which are also discussed in the text have had the characteristics of the solid-state devices fabricated from them discussed elsewhere. [2] In this Supplementary Material, we will refer to the [2]rotaxane and its controls, using the descriptors [2]Ra, [2]Rb, and [2]Rc, and Dba as defined in Figure A1. The [2]R label refers to a [2]rotaxane, meaning that the molecule consists of two mechanically interlocked molecular components –– a dumbbell encircled by a ring. DBa, which refers to the dumbbell of [2]Ra, was also utilized as a control. The large stoppers – one hydrophobic and the other hydrophilic – at either end of the molecules, not only make them amphiphilic, but also lend a relatively large area/molecule in a Langmuir-Blodgett (LB) molecular monolayer film. In this discussion, we will first present a summary of what the measured solution-phase switching mechanisms of these molecules. We will then discuss their performance within a solid-state device.