Molecular Engineering and Measurements To Test Hypothesized Mechanisms in Single Molecule Conductance Switching

Abstract

Six customized phenylene-ethynylene-based oligomers have been studied for their electronic properties using scanning tunneling microscopy to test hypothesized mechanisms of stochastic conductance switching. Previously suggested mechanisms include functional group reduction, functional group rotation, backbone ring rotation, neighboring molecule interactions, bond fluctuations, and hybridization changes. Here, we test these hypotheses experimentally by varying the molecular designs of the switches; the ability of the molecules to switch via each hypothetical mechanism is selectively engineered into or out of each molecule. We conclude that hybridization changes at the molecule-surface interface are responsible for the switching we observe.

Molecular, Supramolecular, and Macromolecular Motors and Artificial Muscles

“…Using the electric field between the STM probe tip and the substrate, OPE derivatives with sufficiently large dipole moments can be driven between two states: a high conductance "on" state, in which molecules appear as protrusions of several Ångstroms from the host matrix SAM, and a low conductance "off" state, with molecules either slightly protruding from or at the same apparent height as the matrix in STM images (Figure 2). 39,55,56 Since OPE molecules are more conductive and longer than the dodecanethiolate molecules of the host SAM, they appear as protrusions in STM images (Figure 2a) when oriented near normal to the surface.…”

“…These unique molecular machines based on MIMs working in concert have been incorporated into drug-delivery vehicles, [60][61][62][63][64][65][66] electrochromic systems, 19,[67][68][69][70] and molecular electronic devices. 26,55,[71][72][73][74][75][76][77][78] Switchable rotaxanes are particularly well-suited for use as artificial muscles because of the potential to harness the collective efforts of ensembles of linear molecules to exert linear forces, as opposed to catenanes, which exhibit radial motions. These types of molecules can be designed to expand or to contract linearly in response to different stimuli, such as chemical, 18,79-83 electrochemical, [84][85][86][87][88] and optical stimuli.…”

Design and control of electron transport properties of single molecules

“…Despite of these recent advances, it remains a great challenge to actively control the electron transport in a molecule and to systematically change its behavior from one type to another since this requires not only precise control of molecular structure, but also accurate activation of different electron tunneling processes. Controlling electron transport at the molecular level has important consequences for many applications, such as molecular electronics (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26), biosensors (27), and solar cells (28,29). For certain molecules, change of electron transport properties could take place due to their specific response to the change of molecular conformation or orientation (19)(20)(21)(22)(23)(24)(25), chemical reactions (26), and tautomerization (18).…”

“…Controlling electron transport at the molecular level has important consequences for many applications, such as molecular electronics (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26), biosensors (27), and solar cells (28,29). For certain molecules, change of electron transport properties could take place due to their specific response to the change of molecular conformation or orientation (19)(20)(21)(22)(23)(24)(25), chemical reactions (26), and tautomerization (18). The latter experiment (18) has attracted considerable attention owning to the facts that the switching process involved does not result in drastic molecular conformation changes as often occurring in mechanical molecular switches induced by cis-trans isomerization of azobenzene (23)(24)(25), making the process potentially more relevant to applications in memory devices.…”

Three-Terminal Devices to Examine Single-Molecule Conductance Switching

“…Discrete switching has been observed in a number of measurement configurations and molecules [1]. Scanning tunneling microscopy (STM) has been particularly useful in studying this phenomenon by observing molecules of interest assembled at grain boundaries and defects in alkane self-assembled monolayers (SAMs).…”