Electrochemical Switching Research Articles

Digital switching systems based on lateral self-oxidation of aluminum nanofilm processors

Advanced “smart label” systems incorporating digital functions and low temperature dependence were constructed from integrated time-dependent electrochemical switches based on the lateral self-oxidation of nanoscale aluminum films. The processors are capable of controlling an integrated display without need of external power and may be used for low-cost “self-writing smart labels” such as time indicators.

Electrofluorescence switching of tetrazine-modified TiO2 nanoparticles

Highly fluorescent tetrazine-modified TiO2 nanoparticles were prepared by the reaction of triethoxysilane-appended chloroalkoxy tetrazine (ESTZ) with TiO2 nanoparticles through a condensation reaction between the surface hydroxyl groups of an electrode and the silane anchor group of ESTZ. The prepared electrodes were used as robust fluorescent layers for electrochemical fluorescence switching (electrofluorochromism) applications in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a charge balancing mediator. The stable charge balancing mediator, TEMPO, in the electrolyte was found to be essential to reduce the intrinsic electron transport resistance of TiO2 in order to achieve reversible electrofluorescence switching. Furthermore it facilitated a fully reversible electrochemical reaction and provided a sufficient charge balance, which allowed us to realize semiconductor-based electrofluorescence switching with an on/off ratio of 4.0 and cyclability greater than 100 cycles.

White-light electrofluorescence switching from electrochemically convertible yellow and blue fluorescent conjugated polymers

We report the study of the fluorescence switching properties of the conjugated copolymers containing triphenylamine, fluorene, benzo[2,1,3]thiadiazole, and cyclic urea moieties. The copolymers show excellent thermal stability and good solubility in polar organic solvents. While the electrofluorescent device (EFD) of P1 emits yellow light under UV excitation, fluorescence intensity is switched off upon electrochemical oxidation. In addition, the fluorescent behavior of the EFD of P1 can be reversibly switched between the non-fluorescent (oxidized) state and the fluorescent (neutral) state with a superb contrast ratio (If/If0) of 21.4. Furthermore, a white-light electrochemical fluorescence switching device is achieved by blending of P1 (yellow) with P2 (blue). Since the fluorescent conjugated polymers of P1 and P2 have their emission simultaneously quenched under the low working potential, the EFD could show a white–dark state of fluorescence with a high contrast ratio (If/If0) of 14.6.

Electrochemical Switching of Conductance with Diarylethene-Based Redox-Active Polymers

Reversible switching of conductance using redox triggered switching of a polymer-modified electrode is demonstrated. A bifunctional monomer comprising a central electroswitchable core and two bithiophene units enables formation of a film through anodic electropolymerization. The conductivity of the polymer can be switched electrochemically in a reversible manner by redox triggered opening and closing of the diarylethene unit. In the closed state, the conductivity of the modified electrode is higher than in the open state.

Time dependent electrochemical switches based on nanofilm processors

Abstract Advanced “Smart label” systems may be constructed from integrated time-dependent electrochemical switches and display elements based on the lateral self-oxidation of nanoscale aluminum films. We developed electrical switches (ON–OFF and OFF–ON) with short switching times and an adjustable delay before actuation for use in low-cost “self-writing smart labels” that do not require an external power supply, are capable of controlling an integrated display, and may be combined with commercial RFID technology.

Efficient Fluorescence “Turn-On” Sensing of Dissolved Oxygen by Electrochemical Switching

We report on a novel method for sensing oxygen that is based on the use of a perylene diimide dye (1) which is electrochemically reduced to its nonfluorescent dianion form (1(2-)). In the presence of oxygen, the dianion is oxidized to its initial form via an electron-transfer reaction with oxygen upon which fluorescence is recovered. As a result, the fluorescence intensity of the dianion solution increases upon the addition of oxygen gas. Results demonstrate that high sensitivity is obtained, and the emission intensity shows a linear correlation with oxygen content (0.0-4.0% v/v) at ambient barometric pressure. In addition, using electrochemical reduction, oxygen determination becomes regenerative, and no significant degradation is observed over several turnovers. The limit of detection is 0.4% oxygen in argon gas.

Electrochemical fluorescence switching properties of conjugated polymers composed of triphenylamine, fluorene, and cyclic urea moieties

AbstractThe study of the electrochemical fluorescence switching properties of the conjugated copolymers containing fluorene, triphenylamine, and 1,3‐diphenylimidazolidin‐2‐one moieties is reported. The polymers show high fluorescence quantum yields, excellent thermal stability, and good solubility in polar organic solvents. While the polymer emits blue light under UV irradiation, the fluorescence intensity is quenched upon electrochemical oxidation. The fluorescent behavior can be reversibly switched between nonfluorescent (oxidized) state and strong fluorescence (neutral) state with a high contrast ratio (If/If0) of 16.3. The role of the electrochemical oxidation of the triphenylamine moieties is to generate the corresponding radical cations that lead to fluorescence quenching in the solid matrix. © 2012 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym Chem, 2012

Highly-Efficient Gating of Solid-State Nanochannels by DNA Supersandwich Structure Containing ATP Aptamers: A Nanofluidic IMPLICATION Logic Device

Integrating biological components into artificial devices establishes an interface to understand and imitate the superior functionalities of the living systems. One challenge in developing biohybrid nanosystems mimicking the gating function of the biological ion channels is to enhance the gating efficiency of the man-made systems. Herein, we demonstrate a DNA supersandwich and ATP gated nanofluidic device that exhibits high ON-OFF ratios (up to 10(6)) and a perfect electric seal at its closed state (~GΩ). The ON-OFF ratio is distinctly higher than existing chemically modified nanofluidic gating systems. The gigaohm seal is comparable with that required in ion channel electrophysiological recording and some lipid bilayer-coated nanopore sensors. The gating function is implemented by self-assembling DNA supersandwich structures into solid-state nanochannels (open-to-closed) and their disassembly through ATP-DNA binding interactions (closed-to-open). On the basis of the reversible and all-or-none electrochemical switching properties, we further achieve the IMPLICATION logic operations within the nanofluidic structures. The present biohybrid nanofluidic device translates molecular events into electrical signals and indicates a built-in signal amplification mechanism for future nanofluidic biosensing and modular DNA computing on solid-state substrates.

Electrochemical Switching of Conformation of Random Polyampholyte Brushes Grafted onto Polypyrrole

We demonstrate the possibilities for subtle control over redox-driven surface switching that could be obtained by altering the balance between hydrophobic, ionic, and dipolar components of polymer brushes that are grafted onto electrochemically active conducting polymers (ECP). We extend our previous work on the conformation switching of polyzwitterionic brushes grafted onto ECP to the case of ABC random polyampholyte brushes: here, a statistical near-neutral copolymer of methyl methacrylate (MMA), methacryloxyethyltrimethylammonium chloride (METAC), and 3-sulfopropyl methacrylate potassium salt (SPMA). The statistical polyampholyte differs from the polyzwitterion in that it is not strictly neutral and the charges do not have a defined spatial relationship to one another. The consequence is a significant change in the switching behavior that is also dependent on the salt concentration in the electrolyte. The results can be understood by reference to the theory of polyampholyte conformation in solution given by Higgs and Joanny modified to apply to a surface-bound brush. Three states of the polyampholyte brush are deduced from electrochemical impedance spectroscopy (EIS): collapsed, partially collapsed, and expanded. At low salt concentration, the behavior was the opposite of that of the polyzwitterion: the brush switched between partially collapsed with the ECP reduced and expanded with the ECP oxidized. With increase of salt concentration, the switch changed, to collapsed with the ECP oxidized and partially collapsed with ECP reduced. At still higher salt concentration, the switch changed back again, to partially collapsed with the ECP reduced and expanded with the ECP oxidized. Measurements of surface wetting under electrochemical control supported the interpretation. The behavior can be contrasted with that of zwitterionic brushes, which show a switch between collapsed with ECP oxidized and expanded with ECP reduced, independent of salt concentration over the same range (10(-3)-2 M NaCl) as that studied here, and that of zwitterionic-hydrophobic block copolymers where the switch is suppressed at low salt concentration. The results illustrate the significant range of behavior that can be engineered into these electrochemically switchable systems.

I-Motif based pH induced electrochemical switches

Two C-rich DNA strands are employed to fabricate the intermolecular i-switch: strand 1 with thiol at the 5′-terminus immobilized on the gold electrode through the thiol–Au interaction, and ferrocene (Fc)-labeled strand 2 that hybridizes with strand 1 to form an i-switch nanostructure. In neutral or basic aqueous solution, the i-switch is present in the form of an extended duplex that makes Fc far away from the electrode; a weak faradaic current is obtained, so-called “OFF” state. While in the slight acidic condition, an obvious signal is detected from Fc which approaches the electrode due to the formation of the i-motif, so‐called “ON” state. The faradaic current has a linear relationship with the pH value in the range of 5.8–8.0.

Controlling Surface Plasmon Optical Transmission with an Electrochemical Switch Using Conducting Polymer Thin Films

AbstractSurface plasmon resonance (SPR)‐enhanced optical transmission is actively controlled by an electrochromism of conducting polymer thin films. Polyaniline and poly(3,4‐ethylenedioxythiophene) thin films are deposited on a thin gold grating surface. SPR‐enhanced optical transmission is demonstrated by irradiating white light on the conducting polymer thin film–gold grating surface and detecting the transmitted light from the back side. The transmission SPR system is combined with an electrochemical setup to manipulate the resonance. The wavelength of the sharp peak in the transmission light spectra is tuned by electrochemical doping/dedoping of the conducting polymer thin films. The present study of controllable SPR‐enhanced optical transmission should provide novel active plasmonic devices such as active bandpass filters or biosensors.

Temperature-Controlled Electrochemical Switch Based on Layered Double Hydroxide/Poly(N-Isopropylacrylamide) Ultrathin Films Fabricated via Layer-by-Layer Assembly

In this paper we report the fabrication of layered double hydroxide (LDH) nanoparticles/poly(N-isopropylacrylamide) (pNIPAM) ultrathin films (UTFs) via the layer-by-layer assembly technique, and their switchable electrocatalytic performance in response to temperature stimuli was demonstrated. X-ray diffraction and UV-vis absorption spectroscopy indicate a periodic layered structure with uniform and regular growth of the (LDH/pNIPAM)(n) UTFs; an interaction based on hydrogen bonding between LDH nanoparticles and pNIPAM was confirmed by X-ray-photoelectron spectroscopy and Fourier transform infrared spectroscopy. Temperature-triggered cyclic voltammetry and electrochemical impedance spectroscopy switch for the UTFs was obtained between 20 and 40 °C, accompanied by reversible changes in surface topography and film thickness revealed by atomic force microscopy and ellipsometry, respectively. The electrochemical on-off property of the temperature-controlled (LDH/pNIPAM)(n) UTFs originates from the contraction-expansion configuration of pNIPAM with low-high electrochemical impedance. In addition, a switchable electrocatalytic behavior of the (LDH/pNIPAM)(n) UTFs toward the oxidation of glucose was observed, resulting from the temperature-controlled charge transfer rate. Therefore, this work provides a facile approach for the design and fabrication of a well-ordered command interface with a temperature-sensitive property, which can be potentially applied in electrochemical sensors and switching.

Reversible Copper(II)/(I) Electrochemical Potential Switching Driven by Visible Light-Induced Coordinated Ring Rotation

We here describe the first metal complex system in which electronic signals can be repeatedly extracted by converting bistable states related to an intramolecular ligand rotational motion, which is fueled by visible light. The molecular structure for relating an electron transfer and a motion consists of a copper center and a coordinated unsymmetrically substituted pyrimidine derivative, whose rotational isomerization causes an electrochemical potential shift. To harness light energy effectively through metal-to-ligand charge transfer (MLCT) excitation, we prepared a simple copper(I) complex coordinated by a 4-methyl-2-(6'-methyl-2'-pyridyl)pyrimidine and a bulky diimine. The thermodynamic and kinetic parameters of redox and rotational reactions were analyzed by cyclic voltammograms at variable temperatures, by considering four stable isomers related to copper(II)/(I) states and rotational isomeric states. The key feature of this compound is that the rotation is frozen in the copper(I) state (rate constant for the rotation, k(Ii→o) = 10(-4) s(-1)) but is active in the copper(II) state (k(IIi→o) = 10(-1) s(-1)) at 203 K. The compound makes a bypass route to the isomeric metastable copper(I) state, via a tentative copper(II) state formed by photoelectron transfer (PET) in the presence of a redox mediator, decamethylferrocenium ion (DMFc(+)), or upon a partial oxidation of the complex. Light- and heat-driven rotation in the copper(I) state with a potential shift (ΔE°' = 0.14 V) was analyzed by electrochemical measurements of the complex in the solution state. The rotor could be reset to the initial state by heating, thereby completing the cycle and enabling repeated operation fueled by light energy. A significant redox potential shift associated with the copper(II)/(I) transition accompanied the rotation, thereby providing a new type of molecular signaling system.

A pH-controllable electrochemical molecule switch employing a new electrochemical measurement system as switching transducer

A new design concept of electrochemical pH-controllable molecular switch is presented by utilizing a new electrochemical measurement system as switching transducer. A pH sensor is connected in series between the terminal points of the working and counters electrodes of a potentisostat, and immersed in the solution together with a reference electrode, establishing a novel electrochemical measurement system. In this system, the variation of pH-controllable interface potential at the pH-sensing film/solution interface can be converted to current response when amperometry technique is employed. Based on this unique current–potential relationship, a pH-controllable switch is designed to monitor the protonation and deprotonation reaction of pH-sensing molecule. The current direction interchanges between positive and negative via pH control, illustrating a reversible conformation transition between protonated state and deprotionated state of molecule. The magnitude of current value represents the degree of protonation and deprotonation reaction of molecule. The strategy is successfully demonstrated with a remarkably reversible polyaniline-based pH-controllable switch, which confirms the feasibility of the novel electrochemical measurement system as switching transducer for designing electrochemical pH-controllable switches. This study may open up a potential avenue to construct the electrochemical pH-controllable switches.

Reversible Electrochemical Switching of Polymer Brushes Grafted onto Conducting Polymer Films

We demonstrate the electrochemical switching of conformation of surface-bound polymer brushes, by grafting environmentally sensitive polymer brushes from an electrochemically active conducting polymer (ECP). Using atom transfer radical polymerization (ATRP), we grafted zwitterionic betaine homopolymer and block copolymer brushes of poly(3-(methacryloylamido)propyl)-N,N'-dimethyl(3-sulfopropyl)ammonium hydroxide) (PMPDSAH) and poly(methyl methacrylate)-b-PMPDSAH, from an initiator, surface-coupled to a poly(pyrrole-co-pyrrolyl butyric acid) film. The changes in ionic solution composition in the surface layer, resulting from oxidation and reduction of the ECP, trigger a switch in conformation of the surface-bound polymer brushes, demonstrated here by electrochemical impedance spectroscopy (EIS) and in a change of wettability. The switch is dependent upon temperature in a way that is analogous to the temperature-dependent solubility and aggregation of similar betaine polymers in aqueous solution but has a quite different dependence on salt concentration in solution. The switch is fully reversible and reproducible. We interpret the switching behavior in terms of a transition to a "supercollapsed" state on the surface that is controlled by ions that balance the charge state of the ECP and are adsorbed to the opposite charges of the zwitterionic graft, close to the graft-ECP interface. The behavior is significantly modified by hydrophobic interactions of the block copolymer graft. We speculate that the synergistic combination of properties embodied in these "smart" materials may find applications in electrochemical control of surface wetting and in the interaction with biomolecules and living cells.

An Elastomeric Poly(Thiophene‐EDOT) Composite with a Dynamically Variable Permeability Towards Organic and Water Vapors

AbstractAn interpenetrating polymer network (IPN) material with controllable nanoporosity is developed for applications such as chemical protection. The IPN material is based on a conducting polymer backbone consisting of thiophene and 3,4 ethylenedioxythiophene (EDOT) repeat units–poly(thiophene‐EDOT)–formed within a soft polyurethane support. The IPN demonstrates reversible, electrochemically switchable nanoporosity in the absence of standard liquid electrolyte, with the oxidized state being the open (high porosity) state and the reduced state being the closed (low porosity) state. The switching of the IPN between its oxidized (open) and reduced (closed) states is actuated using application of ±1.0 V. The variability in the IPN porosity, induced by the electrochemical switching, is revealed by large changes in water vapor diffusivity, as well as changes in the diffusivities of the chemical agent simulants chloroethyl ethyl sulfide (CEES) and methyl salicylate (MeS). The closed state of the IPN is able to decrease CEES diffusivity by ≈99% compared to expanded Teflon (ePTFE), while the open state allows high MVT rates comparable to ePTFE. The IPN's ability to allow high MVT under non‐threat conditions (open state) and high protection from agents under threat conditions (closed state) is a unique and desirable characteristic of this novel IPN material.

PH-, Sugar-, and Temperature-Sensitive Electrochemical Switch Amplified by Enzymatic Reaction and Controlled by Logic Gates Based on Semi-Interpenetrating Polymer Networks

Phenylboronic acid (PBA) moieties are grafted onto the backbone of poly(acrylic acid) (PAA), forming the PAA-PBA polyelectrolyte. The semi-interpenetrating polymer network (semi-IPN) films composed of PAA-PBA and poly(N,N-diethylacrylamide) (PDEA) were then synthesized on electrode surface with entrapped horseradish peroxidase (HRP), designated as PDEA-(PAA-PBA)-HRP. The films demonstrated reversible pH-, fructose-, and thermo-responsive on-off behavior toward electroactive probe K(3)Fe(CN)(6) in its cyclic voltammetric (CV) response. This multiswitchable CV behavior of the system could be further employed to control and modulate the electrochemical reduction of H(2)O(2) catalyzed by HRP immobilized in the films with K(3)Fe(CN)(6) as the mediator in solution. The responsive mechanism of the system was also explored and discussed. The pH-sensitive property was attributed to the electrostatic interaction between the PAA component of the films and the probe at different pH; the thermo-responsive behavior originated from the structure change of PDEA hydrogel component of the films with temperature; the fructose-sensitive property was ascribed to the structure change of the films induced by the complexation between the PBA constituent and the sugar. This smart system could be used as a 3-input logic network composed of enabled OR (EnOR) gates in chemical or biomolecular computing by combining the multiresponsive property of the films and the amplification effect of bioelectrocatalysis and demonstrated the potential perspective for fabricating novel multiswitchable electrochemical biosensors and bioelectronic devices.

Electrical switching of microgel swelling and collapse for display applications

We investigate whether a high-contrast electronic paper can be formed using a microgel dispersion in which the particles reversibly swell and collapse on cycling the pH. An aqueous dispersion of particles of poly(2-vinylpyridine) crosslinked with divinylbenzene is studied. It is demonstrated that the pH of the dispersion, and hence the state of the microgel particles, can be potentiostatically controlled using a polyaniline electrode. Electrochemical switching of the dispersion from highly scattering to transparent for all visible wavelengths is achieved. Modification of cell and electrode design is required to reduce the switching time, presently greater than 10 min. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Switchable surfaces of electroactive polymer brushes grafted from polythiophene ATRP-macroinitiator

Brush copolymers based on polyterthiophene have been synthesized with the aim of using them as electrically responsive layers in smart surfaces. A novel terthiophene monomer, which is polymerizable both chemically and electrochemically, was used to polymerize polyterthiophene backbones as precursors for grafting of sidechains. The precursor polymer is equipped with a bromoester, making it suitable for use as a macroinitiator for Atom Transfer Radical Polymerization (ATRP) of polystyrene-b-polyacrylate branches. In this paper we present the synthesis and characterization of this conductive poly(3′-(ethyl-2-bromopropionate)-2,2′:5′,2″-terthiophene)-g-(polystyrene-b-poly acrylic acid) (PBrTTh-g-(PS-b-PAA)) brush copolymer and demonstrate its reversible switching between conducting and insulating states, with accompanying changes in physical properties. We characterize morphological changes driven by the electrochemical switch with scanning electron microscopy and observe a microscale wetting–dewetting transition of brush copolymer films on the electrode.

Electrochemical ferroelectric switching: Origin of polarization reversal in ultrathin films

Against expectations, robust switchable ferroelectricity has been recently observed in ultrathin (1 nm) ferroelectric films exposed to air [V. Garcia et al., Nature (London) 460, 81 (2009)]. Based on first-principles calculations, we show that the system does not polarize unless charged defects or adsorbates form at the surface. We propose electrochemical processes as the most likely origin of this charge. The ferroelectric polarization of the film adapts to the external ionic charge generated on its surface by redox processes when poling the film. This, in turn, alters the band alignment at the bottom electrode interface, explaining the observed tunneling electroresistance. Our conclusions are supported by energetics calculated for varied electrochemical scenarios.