Improvements in purification of silver nanowires by decantation and fabrication of flexible transparent electrodes. Application to capacitive touch sensors.

Transparent flexible electrodes made of metallic nanowires, and in particular silver nanowires (AgNWs), appear as an extremely promising alternative to transparent conductive oxides for future optoelectronic devices. Though significant progresses have been made the last few years, there is still some room for improvement regarding the synthesis of high quality silver nanowire solutions and fabrication process of high performance electrodes. We show that the commonly used purification process can be greatly simplified through decantation. Using this process it is possible to fabricate flexible electrodes by spray coating with sheet resistance lower than 25 Ω sq⁻¹ at 90% transparency in the visible spectrum. These electrodes were used to fabricate an operative transparent flexible touch screen. To our knowledge this is the first reported AgNW based touch sensor relying on capacitive technology.

Selective Colorimetric Detection of Novichok Agents with Hydrazone Chemosensors.

Novichok is a recently identified class of neurotoxic organophosphorus compounds that have subsequently been banned by the Organization for Prohibition of Chemical Weapons (OPCW) as chemical warfare agents. Selective, rapid detection of Novichok remains a challenge. Several colorimetric paper-based detection devices have recently been developed for the rapid and selective detection of sarin, VX, and sulfur mustard. In this article, we present a similar colorimetric device designed specifically for the detection of Novichok, based on hydrazone derivatives from 2,4-dinitrophenylhydrazine (2,4-DNPH) impregnated on a glass fiber substrate. Results show that these compounds rapidly and selectively reveal the presence of Novichok agents to the naked eye. The low cost, ease of use, portability, and high selectivity to Novichok of this device complete the detection range of colorimetric paper-based sensors for chemical warfare agents.

All-Polymeric Flexible Transparent Heaters.

All-polymeric flexible transparent heaters (THs) are demonstrated for the first time. Thin films of four poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials embedding different dopants exhibit low sheet resistances, down to 57 Ω sq-1 associated with good transparencies (>87%) and a haze lower than 1%. These transparent thin films show excellent heating properties, with high heating rates (up to 1.6 °C s-1) and steady-state temperatures exceeding 100 °C when subjected to 12 V bias. Very high areal power densities were also measured, reaching almost 10 000 W m-2. The temperature increase is finely fitted to a thermal model. It is further demonstrated that these new THs can be efficiently integrated for applications in thermochromic displays and visor deicers.

A star-shaped ruthenium complex with five ferrocenyl-terminated arms bridged by trans-platinum fragments.

We present the synthesis of the new heteropolytopic penta(4-ethynylphenyl)cyclopentadiene ligand, its complexation through the Cp ring to ruthenium tris(indazolyl)borate and through the terminal alkyne groups to five ferrocenyl ethynyl platinum units, yielding an undecanuclear heterotrimetallic complex.

Metallic behaviour of acid doped highly conductive polymers.

Conductive polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) are used in a wide range of applications as transparent electrodes, hole injecting layers or thermoelectric materials for room-temperature applications. However, progress is needed to enhance the electrical conductivities of the materials and to provide understanding about their structure-transport relationships. This work presents the synthesis of highly conductive PEDOT-based polymers using iron(iii) trifluoromethanesulfonate as oxidant for the first time. The metallic behaviour of the polymer is revealed by conductivity monitoring from 3 to 300 K. The electrical conductivity is further improved (to 2273 S cm-1) using acids, leading to a positive temperature coefficient of resistivity at an unprecedented 45.5% oxidation state. X-ray photoemission spectroscopy (XPS) and time of flight-secondary ion mass spectrometry (ToF-SIMS) analyses demonstrate a complete replacement of the trifluoromethanesulfonate anions by hydrogen sulphate counter ions. This substitution results in an increased concentration of charge carriers (measured in organic electrochemical transistors) along with an enhancement of the mean size of crystalline domains, highlighted by small and wide angle X-ray scattering (SAXS/WAXS), which explains the 80% increase of electrical conductivity.

Technomimetic molecules: synthesis of ruthenium(II) 1,2,3,4,5-penta(p-bromophenyl)cyclopentadienyl hydrotris(indazolyl)borate, an organometallic molecular turnstile.

A short route to prepare a ruthenium complex with a pentaphenyl substituted cyclopentadienyl and a hydrotris(indazolyl)borate ligand is described: this complex can be seen as an organometallic molecular turnstile.

Chromogenic detection of Sarin by discolouring decomplexation of a metal coordination complex.

An innovative chromogenic sensing concept based on decomplexation of a tris-(bipyridine)iron(II) coordination complex has been developed for the detection of organophosphorus nerve agents. It was evaluated both on a simulant and real Sarin in vapour and liquid phases.

Development of an autonomous detector for sensing of nerve agents based on functionalized silicon nanowire field-effect transistors.

The ability to detect minute traces of chemical warfare agents is mandatory both for military forces and homeland security. Various detectors based on different technologies are available but still suffer from serious drawbacks such as false positives. There is still a need for the development of innovative reliable sensors, in particular for organophosphorus nerve agents like Sarin. We report herein on the fabrication of a portable, battery-operated, microprocessor-based prototype sensor system relying on silicon nanowire field-effect transistors for the detection of nerve agents. A fast, supersensitive and highly selective detection of organophosphorus molecules is reported. The results show also high selectivity in complex mixtures and on contaminated materials.

Chemical functionalization of electrodes for detection of gaseous nerve agents with carbon nanotube field-effect transistors.

An innovative sensor for the detection of nerve agents in the gas phase based on a carbon nanotube field-effect transistor was developed. A high sensitivity to organophosphorus gases was obtained by modifying gold electrodes with specific tailor-made self-assembled monolayers.

Highly end-doped silicon nanowires for field-effect transistors on flexible substrates.

We report on the VLS (vapour-liquid-solid) fabrication and characterization of in situ axially doped silicon nanowires (SiNWs) at both ends, and on their integration into a bottom gate-top contact geometry on both rigid and flexible substrates to realize field-effect transistors (FETs). To improve contact resistance between SiNWs and source/drain electrodes, we axially tuned the level of doping at both ends of the SiNWs by sequential in situ addition of PH(3). Characterisation of SiNWs by scanning spreading resistance microscopy in the device configuration allowed us to determine precisely the different sections of the SiNWs. The transfer to flexible substrates still allowed for workable FET structures. Transistors with electron mobilities exceeding 120 cm(2) V(-1) s(-1), I(on)/I(off) ratios greater than 10(7) and ambipolar behaviour were achieved.

Prototypes of molecular motors based on star-shaped organometallic ruthenium complexes.

This tutorial review presents our strategy to control the rotation in a molecular rotary motor, and the family of star-shaped ruthenium complexes designed to perform such a task. The molecules have a piano-stool structure with a "stator" meant to be grafted on a surface, and a "rotor" bearing redox-active groups, so that addressing the molecule with nano-electrodes would trigger rotation.

Synthesis and reactivity of [penta(4-halogenophenyl)cyclopentadienyl][hydrotris(indazolyl)borato]ruthenium(II) complexes: rotation-induced Fosbury flop in an organometallic molecular turnstile.

The preparation of ruthenium(II) complexes coordinated to a penta(4-halogeno)phenylcyclopentadienyl ligand and to the hydrotris(indazolyl)borate ligand are detailed. Our strategy involves first the coordination of the penta(4-bromo)phenylcyclopentadienyl ligand by reaction with the ruthenium-carbonyl cluster followed by the coordination of the tripodal ligand. The pentabrominated precursor was successfully converted to the pentaiodinated derivative by using the Klapars-Buchwald methodology, applied for the first time on organometallic substrates. Cross-coupling reactions were performed on both pentabromo and pentaiodo complexes to introduce in a single step the five peripheric ferrocenyl fragments required to obtain a potential molecular motor. The two ligands present in the ruthenium complexes undergo a correlated rotation that was established both experimentally by NMR experiments and an X-ray diffraction study, and theoretically by DFT calculations. The potential-energy curve obtained by DFT revealed the energy barrier of the gearing mechanism to be only 4.5 kcal mol(-1). These sterically highly constrained complexes can be regarded as organometallic molecular turnstiles.

Electron-triggered motions in technomimetic molecules.

Technomimetic molecules are molecules designed to imitate macroscopic objects at the molecular level, also transposing the motions that these objects are able to undergo. This article focuses on technomimetic molecules with motions triggered by electrons. The first part is devoted to our work in the field of molecular switches: after having demonstrated the possibility of controlling an intramolecular electron transfer by photoisomerisation, we are now trying to control the isomerisation, either by electrochemistry, or by embedding the photochromic compound in a self-assembled monolayer and testing the electrical conduction with a STM tip. In a second part, we present our strategy on controlling the rotation in a molecular rotary motor and the family of ruthenium complexes designed to perform such a task. The molecules have a piano-stool structure with a "stator" meant to be grafted on an oxide surface, and a "rotor" bearing redox-active groups, so that addressing the molecule with nano-electrodes would trigger rotation. The electrical control of the charge state of a molecule by a STM tip is developed in a final part.

Heterocyclic alpha-helix mimetics for targeting protein-protein interactions.

The design and synthesis of alpha-helix peptidomimetics using inverse electron demand Diels-Alder reactions is described. The potency of the resulting pyridazine-based library to disrupt the Bak/Bcl-X(L) interaction was tested using an in vitro fluorescence polarization assay.