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Artificial Molecular Machines.

Erbas-Cakmak S, Leigh DA, McTernan CT, Nussbaumer AL - Chem. Rev. (2015)

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Affiliation: School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.

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bonded molecules and on catenanes and rotaxanes in which switching of other protic solvents... This effect (listed in descending binding ability) stations on the thread, macrocycle In these systems, fast-responding reporters are preferred... practical applications by utilizing molecular scale changes to create macroscopic effects... The thread of these rotaxanes included an anthracene fluorophore similar application in synthetic polymers often furnishes a useful result... of Brownian motion can be exploited to great effect in the synthesis every aspect of functional molecule and materials design... An improved robotics” in which ratcheted motions of molecular components

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(a) Rotaxane 149-based molecular switch tunnel junctionsand proposed mechanism for the operation. (i) In the ground state,the tetracationic cyclophane (dark blue) mainly encircles the TTFstation (green) and the junction exhibits low conductance. (ii) Applicationof a positive bias results in one- or two-electron oxidation of theTTF units (green → pink), and increases electrostatic repulsioncausing (iii) shuttling of the macrocycle to the DNP station (red).(iv) Returning the bias to near −0 V provides a high conductancestate, in which the TTF units have been regenerated, but translocationof the cyclophane has not yet occurred due to a significant activationbarrier to movement. Thermally activated decay of this metastablestate may occur slowly ((iv) → (i), in a temperature-dependentmanner) or can be triggered by the application of a negative voltage(v), which temporarily reduces the cyclophane to its diradical dicationform (dark blue → orange), allowing facile recovery of thethermodynamically favored coconformation (vi). (b) Example of onedesign of a molecular switch. The coloring of the functional unitscorresponds to that used for the structural diagrams.1479,1482,1483 Reprinted with permission fromref (14). Copyright2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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fig60: (a) Rotaxane 149-based molecular switch tunnel junctionsand proposed mechanism for the operation. (i) In the ground state,the tetracationic cyclophane (dark blue) mainly encircles the TTFstation (green) and the junction exhibits low conductance. (ii) Applicationof a positive bias results in one- or two-electron oxidation of theTTF units (green → pink), and increases electrostatic repulsioncausing (iii) shuttling of the macrocycle to the DNP station (red).(iv) Returning the bias to near −0 V provides a high conductancestate, in which the TTF units have been regenerated, but translocationof the cyclophane has not yet occurred due to a significant activationbarrier to movement. Thermally activated decay of this metastablestate may occur slowly ((iv) → (i), in a temperature-dependentmanner) or can be triggered by the application of a negative voltage(v), which temporarily reduces the cyclophane to its diradical dicationform (dark blue → orange), allowing facile recovery of thethermodynamically favored coconformation (vi). (b) Example of onedesign of a molecular switch. The coloring of the functional unitscorresponds to that used for the structural diagrams.1479,1482,1483 Reprinted with permission fromref (14). Copyright2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mentions: In a series of ground-breakingbut controversial experiments interfacingswitchable rotaxanes and catenanes with silicon-based electronics,molecular shuttles have been employed in solid-state molecular electronicdevices.1146,1477−1485 Bistable [2]rotaxanes and [2]catenanes have been the subject ofnumerous experimental investigations in the course of the developmentof such molecular electronic devices.1233,1478,1486−1495 Here, the bistable [2]catenanes and [2]rotaxanes feature a cyclobis(paraquat-p-phenylene) (CBPQT4+) macrocycle and two stations,often a tetrathiafulvalene (TTF) site and a dioxynaphtalene site (DNP).Initially the macrocycle preferentially resides over the TTF sitedue to strong aromatic charge-transfer interactions between the components;this is referred to as the ground-state coconformation (GSCC). Electrochemicaloxidation of the TTF station to form TTF2+ generates Coulombicrepulsion between CBPQT4+ and TTF2+, and drivesthe translation of the macrocycle to the DNP station, to give themetastable state coconformation (MSCC). The process can be reversedon reduction of TTF2+ to TTF followed by either thermalrelaxation of the macrocycle to the TTF station, or reduction of thebipyridinium units in the cyclophane ring to the corresponding radicalcations, which reduces the activation barrier to shuttling, restoringthe system to the GSCC. These two mechanically distinguishable statesexhibit different characteristic tunneling currents. On the basisof quantum mechanical computational studies, the MSCC state is predictedto be the more highly conducting state. The switching cycle can bedetected by a number of experimental techniques including time- andtemperature-dependent electrochemistry and spectroscopy. Studies haveshown that current levels on switching are influenced by temperature,the structure of the rotaxane/catenane, and the environment in whichthe molecular machines are embedded.1496−1498 Different environments,including Langmuir–Blodgett (LB) films,1499−1501 self-assembled monolayers (SAMs),1502−1506 and solid-state molecular-switch tunneljunctions (MSTJs), have been extensively studied.1150,1151,1488,1489,1507−1512 In one particular MSTJ, a monolayer of switchable rotaxane 149 was embedded between two conducting electrodes (Figure 60). This MSTJ actsas a gate, which can be opened or closed in response to an appliedvoltage by changes in conductivity and resistance and could be usedin molecular logic gate designs. The reported design showed stableswitching voltages of −2 and +2 V, with reasonable on/off ratiosand low switch-closed currents. Nanometer-scale devices have beenbuilt using this approach and connected to form 2-D crossbar circuitarchitectures.1144 As a next step, theauthors published the design of a 160-kilobit molecular electronicmemory circuit consisting of 400 silicon-nanowire electrodes (16 nmwide) and crossed by 400 Ti electrodes sandwiching a monolayer ofbistable [2]rotaxanes.1513 Despite theinteresting findings, many remain skeptical about the utility of rotaxanesin electronics, and an array of scientific and engineering challengesremain to be addressed such as device robustness, improved etchingtools, and improved switching speed.1514−1516


Artificial Molecular Machines.

Erbas-Cakmak S, Leigh DA, McTernan CT, Nussbaumer AL - Chem. Rev. (2015)

(a) Rotaxane 149-based molecular switch tunnel junctionsand proposed mechanism for the operation. (i) In the ground state,the tetracationic cyclophane (dark blue) mainly encircles the TTFstation (green) and the junction exhibits low conductance. (ii) Applicationof a positive bias results in one- or two-electron oxidation of theTTF units (green → pink), and increases electrostatic repulsioncausing (iii) shuttling of the macrocycle to the DNP station (red).(iv) Returning the bias to near −0 V provides a high conductancestate, in which the TTF units have been regenerated, but translocationof the cyclophane has not yet occurred due to a significant activationbarrier to movement. Thermally activated decay of this metastablestate may occur slowly ((iv) → (i), in a temperature-dependentmanner) or can be triggered by the application of a negative voltage(v), which temporarily reduces the cyclophane to its diradical dicationform (dark blue → orange), allowing facile recovery of thethermodynamically favored coconformation (vi). (b) Example of onedesign of a molecular switch. The coloring of the functional unitscorresponds to that used for the structural diagrams.1479,1482,1483 Reprinted with permission fromref (14). Copyright2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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fig60: (a) Rotaxane 149-based molecular switch tunnel junctionsand proposed mechanism for the operation. (i) In the ground state,the tetracationic cyclophane (dark blue) mainly encircles the TTFstation (green) and the junction exhibits low conductance. (ii) Applicationof a positive bias results in one- or two-electron oxidation of theTTF units (green → pink), and increases electrostatic repulsioncausing (iii) shuttling of the macrocycle to the DNP station (red).(iv) Returning the bias to near −0 V provides a high conductancestate, in which the TTF units have been regenerated, but translocationof the cyclophane has not yet occurred due to a significant activationbarrier to movement. Thermally activated decay of this metastablestate may occur slowly ((iv) → (i), in a temperature-dependentmanner) or can be triggered by the application of a negative voltage(v), which temporarily reduces the cyclophane to its diradical dicationform (dark blue → orange), allowing facile recovery of thethermodynamically favored coconformation (vi). (b) Example of onedesign of a molecular switch. The coloring of the functional unitscorresponds to that used for the structural diagrams.1479,1482,1483 Reprinted with permission fromref (14). Copyright2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Mentions: In a series of ground-breakingbut controversial experiments interfacingswitchable rotaxanes and catenanes with silicon-based electronics,molecular shuttles have been employed in solid-state molecular electronicdevices.1146,1477−1485 Bistable [2]rotaxanes and [2]catenanes have been the subject ofnumerous experimental investigations in the course of the developmentof such molecular electronic devices.1233,1478,1486−1495 Here, the bistable [2]catenanes and [2]rotaxanes feature a cyclobis(paraquat-p-phenylene) (CBPQT4+) macrocycle and two stations,often a tetrathiafulvalene (TTF) site and a dioxynaphtalene site (DNP).Initially the macrocycle preferentially resides over the TTF sitedue to strong aromatic charge-transfer interactions between the components;this is referred to as the ground-state coconformation (GSCC). Electrochemicaloxidation of the TTF station to form TTF2+ generates Coulombicrepulsion between CBPQT4+ and TTF2+, and drivesthe translation of the macrocycle to the DNP station, to give themetastable state coconformation (MSCC). The process can be reversedon reduction of TTF2+ to TTF followed by either thermalrelaxation of the macrocycle to the TTF station, or reduction of thebipyridinium units in the cyclophane ring to the corresponding radicalcations, which reduces the activation barrier to shuttling, restoringthe system to the GSCC. These two mechanically distinguishable statesexhibit different characteristic tunneling currents. On the basisof quantum mechanical computational studies, the MSCC state is predictedto be the more highly conducting state. The switching cycle can bedetected by a number of experimental techniques including time- andtemperature-dependent electrochemistry and spectroscopy. Studies haveshown that current levels on switching are influenced by temperature,the structure of the rotaxane/catenane, and the environment in whichthe molecular machines are embedded.1496−1498 Different environments,including Langmuir–Blodgett (LB) films,1499−1501 self-assembled monolayers (SAMs),1502−1506 and solid-state molecular-switch tunneljunctions (MSTJs), have been extensively studied.1150,1151,1488,1489,1507−1512 In one particular MSTJ, a monolayer of switchable rotaxane 149 was embedded between two conducting electrodes (Figure 60). This MSTJ actsas a gate, which can be opened or closed in response to an appliedvoltage by changes in conductivity and resistance and could be usedin molecular logic gate designs. The reported design showed stableswitching voltages of −2 and +2 V, with reasonable on/off ratiosand low switch-closed currents. Nanometer-scale devices have beenbuilt using this approach and connected to form 2-D crossbar circuitarchitectures.1144 As a next step, theauthors published the design of a 160-kilobit molecular electronicmemory circuit consisting of 400 silicon-nanowire electrodes (16 nmwide) and crossed by 400 Ti electrodes sandwiching a monolayer ofbistable [2]rotaxanes.1513 Despite theinteresting findings, many remain skeptical about the utility of rotaxanesin electronics, and an array of scientific and engineering challengesremain to be addressed such as device robustness, improved etchingtools, and improved switching speed.1514−1516

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

bonded molecules and on catenanes and rotaxanes in which switching of other protic solvents... This effect (listed in descending binding ability) stations on the thread, macrocycle In these systems, fast-responding reporters are preferred... practical applications by utilizing molecular scale changes to create macroscopic effects... The thread of these rotaxanes included an anthracene fluorophore similar application in synthetic polymers often furnishes a useful result... of Brownian motion can be exploited to great effect in the synthesis every aspect of functional molecule and materials design... An improved robotics” in which ratcheted motions of molecular components

No MeSH data available.


Related in: MedlinePlus